The 34-mile (55km) Hong Kong-Zhuhai-Macau Bridge, which was completed two years behind schedule in 2018, connects Hong Kong, Zhuhai, and Macau, and consists of three bridges, an undersea tunnel, and four artificial islands.

At 34 miles (55km), the megaproject is the world's longest sea-crossing bridge. It also takes the title of the most expensive bridge and tunnel complex ever, costing around $20 billion (£15.2bn) by the time it was completed. It’s unsurprising that the final bill was such a big sum, as an enormous 400,000 tonnes of steel went into building it – the equivalent of 60 Eiffel Towers.

Now discover 30 of the world's most expensive buildings.