When it comes to vital infrastructure, defence, and other critical spending priorities, governments around the world have been known to dig deep, with public money clearly no object.
In fact, the expenditure for some megaprojects can be truly mind-blowing, with grand totals that comfortably stretch into hundreds of billions.
From post-disaster reconstruction efforts to high-speed rail links, read on to discover the astronomical projects that have been fully or partly funded by the state in 28 different countries around the world.
All dollar values in US dollars.
Dublin's new children's hospital is the Irish government's most expensive individual project to date. Once completed, it will also be the world's most expensive medical facility, with costs ballooning from an original estimate of €800 million ($868m/£684m) to €2.24 billion ($2.4bn/£1.9bn) as of February this year.
In August 2023, after Irish health minister Stephen Donnelly said the hospital's completion date had been pushed back, the government was accused of "losing control" of the project.
With substantial completion expected in October, Prime Minister Leo Varadkar has warned the government will not accommodate any additional budget increases, saying €2.24 billion is the "maximum allocation."
A new high-speed rail line linking Lisbon to Porto in just 75 minutes will likely become the most expensive government project in Portuguese history. Initial cost estimates put the project, divided into three phrases and scheduled for completion in 2030, at €4.5 billion ($4.8bn/£4bn).
However, that has already grown to €5.5 billion ($6bn/£4.7bn). Phase 1 of the line, from Porto to Soure, went to tender in early 2024, with the government seeking a public-private partnership worth nearly €2 billion ($2.2bn/£1.7bn) to fund, design and build the initial line.
Government funding, including money from the EU, will cover the remaining costs of the estimated €3.6 billion ($3.9bn/£3.1) Phase 1 work.
Denmark's most expensive government-funded project is the Fehmarn Belt fixed link.
Slated to open in 2029, the 11-mile (18km) road and rail link will connect the Danish island of Lolland to Germany's Fehmarn island and feature the world's longest immersed (as opposed to bored) tunnel.
Denmark is bearing the bulk of the project's €10 billion ($10.9bn/£8.7bn) cost, though it reportedly plans to recoup the expenditure by levying tolls. The EU is contributing €1.1 billion ($1.2bn/£940m) toward the project.
The Brenner Base Tunnel is hands-down the priciest infrastructure project in Austrian history. Fortunately, its estimated €10.5 billion ($11.4bn/£9bn) cost is being shared by Austria, the Italian government, and the EU.
Due for completion in 2032, the Alpine tunnel will connect Innsbruck in Austria with the Italian village of Fortezza. At 34 miles (55km), it's set to be one of the longest rail tunnels in the world.
Creating a new administrative capital from scratch doesn't come cheap, as the Malaysian government is undoubtedly well aware.
Named in honour of the country's first prime minister, work on Putrajaya, located 15 miles (25km) south of Kuala Lumpur, began in 1995. It was declared a federal territory in 2001.
The project cost around $8.1 billion (£6bn), which works out at $14 billion (£11bn) in today's money, and it remains the government's priciest-ever project.
The Singaporean government is ploughing $14.8 billion (£11.8bn) into a vast state-of-the-art mega port. The goal? To nearly double the city-state's handling capacity and cement its position as one of the world's foremost maritime trading hubs.
The project is predicted to take two decades to finish, though the first phase is expected to be completed by 2027.
The Philippines is going all out with the new airport it's constructing for its capital Manila, which is projected to cost $15 billion (£12bn).
With the capacity to handle 100 million passengers a year, the international hub in the Bulacan province to the north of the capital is being built by billionaire Ramon Ang's San Miguel Corporation. It will commence operations in 2027.
Currently the world's longest rail tunnel – not to mention the deepest traffic tunnel – the Gotthard Base Tunnel is Switzerland's largest-ever infrastructure project.
Completed in 2016 for the equivalent of $15 billion (£12bn) in today's money, the 35.5-mile (57km) Alpine tunnel has been hailed a marvel of engineering. Even marvels have their problems, however, and it was recently the scene of a derailment that has resulted in a partial closure.
The Tren Maya ("Maya Train") is President Andrés Manuel López Obrador's flagship project, with the final bill anticipated to be around $20 billion (£16bn). Bloomberg reports that this is around 70% higher than the previously stated cost of the work.
With the goal of boosting tourism, the 950-mile (1,500km) railway will traverse the Yucatán Peninsula, connecting beach destinations and ancient Mayan sites.
Partially opened in December 2023 with limited service, the project hasn't been without its detractors, and it's attracted a barrage of criticism for its impact on the environment.
As South Africa endures a protracted energy crisis, its flagship infrastructure project, which consists of two giant coal-fired power stations, the Kusile and Medupi plants, remains incomplete.
Construction began in 2007 and both power stations were expected to be ready by 2014. However, everything from corruption to technical blunders has led to arduous delays.
Kusile is slowly going online and is expected to be fully operational later this year. Meanwhile, corrections to design defects at Medupi won't be resolved until 2027. Unsurprisingly, costs have spiralled, with the total bill for both plants estimated at an enormous $24.3 billion (£19.1bn) in 2022.
The devastating Christchurch earthquake claimed 185 lives and injured thousands in February 2011, as well as destroying or severely damaging up to 80% of the city centre and much of its infrastructure in the process.
Initially, government officials pledged NZ$8.5 billion ($5bn/£4bn) to rebuild the city. Two years later that had jumped to NZ$15bn ($9.3bn/£7.3bn) with the entire reconstruction effort, which is ongoing, estimated at NZ$40 billion ($24.7bn/£19.4bn).
Canada has a long history of nailing large engineering projects. None of them, however, have eclipsed the cost of Phase 1 of the James Bay Project, which was completed in 1984 by state-owned utility Hydro-Québéc and the government of Québec.
And no wonder. The first phase of the controversial hydroelectric development on the east coast of James Bay, which displaced Cree and Inuit locals, came in at a total of C$13.7 billion, which is $26.6 billion (£21bn) in today's money.
Italy is in the midst of an infrastructure construction boom, having smashed the record for large projects in 2022, with the Turin-Lyon high-speed railway the most costly of them all.
Scheduled for completion in 2032, the 170-mile (270km) rail line will cross the Alps and feature the world's longest train tunnel. Opponents have slammed the project's cost, with the final bill expected to come in at least €25 ($27bn/£21.4bn). Fortunately, Italy is sharing the cost with France and the EU.
Madrid Nuevo Norte, Europe's largest regeneration scheme, is transforming the neglected northern sector of the Spanish capital.
Projected to cost €25.2 billion ($27.4bn/£21.6bn), more than half of which will be put up by the private sector, the sustainability-focussed project encompasses 570 acres (230ha) of brownfield land that will eventually feature gleaming towers, low-rise blocks, and plenty of green space.
Given its scope, the scheme will take over two decades to finish, with an anticipated completion date of 2045.
The most expensive government projects tend to have strong private-sector backing, with Indonesia's proposed new capital city, Nusantara, no exception. In fact, 80% of the $35 billion (£30bn) required to build the city will be provided by private investors.
With Jakarta sinking, the Indonesian government plans to relocate to the island of Borneo, where the future smart city is about to take shape deep in the jungle.
The project is set for completion in 2045, 100 years after Indonesia declared independence from the Netherlands.
Beating grand French infrastructure projects such as the Maginot Line and Channel Tunnel in terms of its sheer cost is the aptly named Grand Paris Express.
This epic undertaking, agreed in 2011, will see the Paris Métro double in size by 2030 and has already involved the drilling of more than 120 miles (190km) of tunnels. The project's cost has mushroomed over the years, and it's now expected to set the French state back by around €36.1 billion ($39bn/£31bn).
The war in Ukraine led to a flurry of defence spending, with a number of countries upping their military expenditure.
In early 2023, the German government said it would allocate an eye-watering €40 billion ($43.4 billion/£34bn) in the years leading up to 2040 to develop a next-generation fighter jet with France.
The jet is part of the €100 billion ($108.4bn/£85.5bn) Future Combat Air System programme established in 2017 between French President Emmanuel Macron and then German Chancellor Angela Merkel.
A plan to replace seven ferry crossings along Norway's west coast with a 700-mile (1,100km) route that features "floating" tunnels and bridges will cost $47 billion (£37bn), according to estimates.
That's if it's ever completed, though. There are reportedly plans to scale back the project due to its surging expense, though it could be re-extended again in the future.
The most expensive government project in Brazilian history is the Itaipu Hydroelectric Dam, the world's second most productive hydroelectric facility. Completed in 1982 and located near the Paraguay border, the engineering wonder cost $19.6 billion (£16bn) at the time, the equivalent of $56.7 billion (£44.7bn) in today's money.
A notable runner-up is the federal capital of Brasília, which was built from scratch in the 1950s. A cost of $1.5 billion was estimated by Brazil's Minister of Finance in 1960, which is $15.3 billion (£12.1bn) in today's money, but others say the exact cost is unknown.
Mired in corruption, the 2014 Winter Olympic Games in Sochi was the most expensive edition of the sporting event by some way, costing a staggering $69.8 billion (£55bn) in today's money.
Money was lavished on the Olympic Village and competition venues, as well as on transport networks, hotels, and power supplies, with the hope of turning Sochi into a destination for tourists.
Private companies shouldered some of the expense. However, a 2015 study suggested Russian taxpayers would be forking out a billion dollars a year for the foreseeable future to cover the Games' debts.
Concerned that the Dubai International Airport could soon reach capacity, airport officials aimed to build the world's largest airport in preparation.
An expansion of the city's smaller Al Maktoum International Airport had started but was halted due to a dip in forecasted visitor numbers. The decision was made after the nation had already spent $33 billion (£26bn) on the first phase, which began in 2010 and initially concentrated on cargo operations.
As Dubai's tourism figures return to pre-pandemic levels, government officials are revisiting plans for expanding the city's second airport, which was previously expected to cost around $80 billion (£63bn).
Melbourne's Suburban Rail Loop is a 56-mile (90km) orbital line that will link the city's central business district with the outer suburbs.
Critics have derided Australia's most extensive infrastructure project, describing it as a "rail loop to nowhere", while the completion date could run as late as 2085.
And it just keeps getting more expensive. Presumably due to increased inflation, the link's estimated cost now stands at a jaw-dropping A$125 billion ($81bn/£64.5bn), significantly up on the A$50 billion ($32.7bn/£25.8bn) proposed in 2018.
Japan has delivered numerous wow-factor infrastructure projects over the years, from the bullet train to the Honshu-Shikoku Bridge.
The most impressive – and expensive – of them all is the clean-up operation undertaken following the 2011 Fukushima nuclear disaster. The nation has already spent $82 billion (£64.7bn) as of 2022.
Sweden's second-largest city, Gothenburg, is currently being treated to the mother of all makeovers.
Between now and 2035, an eye-popping €100 billion ($108bn/£86bn) will be invested in the city's revamp, which will include 105,000 new homes, two new tunnels, an impressive cable car system, and a new bridge in the centre.
No other infrastructure programme in Swedish history comes close in terms of cost.
HS2, the UK's high-speed railway linking London to cities in the centre and north of England, is massively over budget, hugely delayed, and highly divisive.
Initially set to cost $47.5 billion (£37.5bn), the priciest infrastructure project in British history is now expected to burn through $116.5 billion (£92bn), while the first phase connecting London to Birmingham may not be ready until 2033, seven years behind schedule. Meanwhile, plans to add an additional line between London and Leeds, and the extension of the line from Birmingham to Manchester have been scrapped entirely.
Bharatmala Pariyojana (also referred to as the India Garland Project) is India's answer to America's Interstate Highway System project. It involves the construction of a breathtaking 52,000 miles (83,700km) of highways, borders, tunnels, and bridges to create a national network that reflects the country's rapid development.
Initiated in 2017, the project is taking longer than anticipated, like so many of this scale. The first phase was due to be finished in 2022 but is now five years behind schedule.
The cost of the entire project has soared due to the delays and currently stands at nearly $130 billion (£103bn), almost double the original estimate.
Forget the Hoover Dam, Manhattan Project, and Apollo Program: the most expensive government project in US history is actually the development of the Lockheed Martin F-35 Lightning II fighter jet.
The weapons system is a decade behind schedule and 80% over budget, bringing its cost to an almost unimaginable $1.7 trillion (£1.3tn). On the upside, America's allies are clamouring to place orders for the jet, which could make the colossal expense more than worthwhile.
A maritime Silk Road for the 21st century, the Chinese government's Belt and Road Initiative (BRI) is now a decade old and has grown to involve 155 countries.
A trillion dollars has already been spent on the mammoth global infrastructure project, with official estimates suggesting that the ongoing project could cost as much as $8 trillion (£6.2tn).
That said, the BRI has been plagued with problems since its inception and will likely be considerably scaled back as a result.
From megaproject to mega fail: discover the global megaprojects that went seriously wrong