Up for a challenge? An antiques marketplace is offering $1.2 million (£1m) to the first person who can prove the mythical Holy Grail exists. The stuff of legend, the chances of discovering the chalice used in the Last Supper are on a par with finding a pot of gold at the end of a rainbow, but that won't stop some people. Treasure hunting is all the rage right now and metal detector sales are booming. From Nazi gold to missing Fabergé eggs, we take a look at the most epic treasure hunts ever.

First mentioned by the poet Chrétien de Troyes (pictured) in 1190, the Holy Grail was described a century later as the vessel used at the Last Supper and to collect the blood of Christ at the Crucifixion. Thought to be a symbol associated with Arthurian legend rather than a tangible object, needless to say it has never been found.

Whether the priceless vessel is real or not hasn't put people off trying to find it. For centuries, Grail hunters, or 'Grailers', from Richard the Lionheart to Victorian adventurers have sought the fabled object, and popular movies and books like the Monty Python classic, Indiana Jones and the Last Crusade, and Dan Brown's The Da Vinci Code have helped the Holy Grail remain in the public consciousness.

As recently as 2006, Grailers hunted for the chalice under the Basilica of San Lorenzo Fuori le Mura in Rome (pictured) after Italian archaeologist Alfredo Barbagallo claimed it was buried there. Now that LoveAntiques.com is offering $1.2 million (£1m) for hard evidence the grail exists, expect the search to intensify.

Keen to get involved? In addition to the Basilica of San Lorenzo Fuori Le Mura in Rome, possible locations for the Holy Grail that have been suggested over the years include Glastonbury in England, Spain's Montserrat Abbey near Barcelona and the sewers of Old Jerusalem.

The ultimate Easter egg hunt, there are seven lost Fabergé Imperial eggs waiting to be found. The House of Fabergé crafted a total of 50 of these bejeweled masterpieces for the Russian royal family from 1885 up until the eve of the October Revolution in 1917.

Amid the chaos of revolution, the eggs were confiscated by Bolshevik revolutionaries. While some ended up in the Kremlin Armory, others were smuggled out of Russia and sold to the highest bidder or simply stolen and squirreled away or destroyed.

The lost eggs include the 1888 Cherub with Chariot, the Nécessaire from 1889 and the 1903 Royal Danish, each of which could be worth up to $30 million (£24.6m). The Mauve egg, which dates from 1897, is missing but its surprise, a heart-shaped photo frame, has survived. The frame was purchased by Malcolm Forbes in 1978 and sold to the Fabergé Museum in Saint Petersburg, Russia in 2004.

Though there's a chance the lost eggs have been broken up, melted down and lost forever, treasure hunters hoping to get lucky got a glimmer of hope in 2012 when the Third Imperial Egg surfaced at a scrap metal dealership in the American Midwest of all places. It went on to sell for an estimated $33 million (£27m) in 2014.

If you've got a metal detector and spade handy, you might want to make a beeline for Ireland's Wicklow Mountains, not far from Dublin. The Irish Crown Jewels, which were stolen in 1907 in what is regarded as Ireland's most infamous heist, are thought to be buried there.

The jewels, a gemstone-encrusted star and badge of the Order of St. Patrick, as well as five knight's collars, went missing from a safe in Dublin Castle four days before a visit by King Edward VII. Several suspects, including Francis Shackleton, the brother of explorer Ernest Shackleton, were investigated but the culprit was never found and the jewels are still AWOL.

Over the years, plenty of theories have emerged as to the whereabouts of the jewels. Rumors they were smuggled to Paris or the US have circulated but a tip-off received by Irish authorities in 1983 is the strongest lead.

According to the tip-off, the treasure, which is worth $15 million (£12m) in today's money, is buried somewhere in the Wicklow mountains. Ireland's police force the Gardai has carried out searches using metal detectors as recently as 2013, but their efforts have turned up nothing and the jewels remain lost.

The Irish Crown Jewels aren't the only royal crown jewels that have vanished. According to legend, King John of England, the monarch who signed the Magna Carta, lost the nation's Crown Jewels in the silty mud of the Wash on England's east coast back in 1216.

The king was traveling through England's east to quell an uprising when he lost his precious treasures. The hoard is said to include ancient gem-studded crowns, the bejeweled sword of Tristram, a golden wand with a dove, gold goblets, silver plates and thousands of gold coins.

Experts believe the treasure could be worth $70 million (£58m) in today's money. Over the years, three possible locations for the lost Crown Jewels have been narrowed down: around Sutton Bridge, at some point between Wisbech and Walsoken, and somewhere between Walpole and Foul Anchor.

In 2015, archaeologist Ben Robinson surveyed the area for a BBC documentary on King John using state-of-the-art laser and GPS technology. The survey uncovered silt movement patterns and not much else, and Robinson concluded that the chance of finding the Old Crown Jewels of England, which are likely to be buried under layers of silt, is akin to finding a needle in a haystack.

Regarded as the 'Eighth Wonder of the World', the breathtaking Amber Room was created for King Frederick of Prussia in the early 18th century. An opulent chamber of exquisite amber panels backed with gold leaf and ornate mirrors, the Amber Room went missing towards the end of World War II.

Worth an estimated $303 million (£250m) in today's money, the Amber Room was the star attraction of the Catherine Palace near Leningrad, now Saint Petersburg, in Russia. Shortly before the Nazi invasion of the USSR in 1941, Soviet authorities concealed the room with plain wallpaper in a bid to prevent advancing Nazi troops getting their hands on it.

The attempt to hide the chamber failed miserably and Nazi soldiers dismantled the Amber Room in October 1941. Not long after, the room was transported to Königsberg Castle in Königsberg, East Prussia, now Kaliningrad, Russia, where it was stored until 1945.

The castle was destroyed in 1945 but some experts believe the Amber Room was removed for safekeeping and at least 15 theories have been put forward as to its whereabouts. Possible locations include the Kaliningrad region, as well as parts of Germany and Poland. In 2004, a replica of the Amber Room was created for the reconstructed Catherine Palace but, to date, the location of the real deal, if it did actually survive the war, remains a mystery.

Gold and jewels worth billions of dollars could well be lying under the streets of Mexico City. On the 'Noche Triste' ('Sad Night') of June 30 1520, Spanish conquistador Hernán Cortés and his troops battled their way out of the Aztec capital Tenochtitlan, the site of the future Mexican capital, following the death of Aztec ruler Montezuma II.

Laden with treasure, the conquistadors attempted a quick getaway but the Aztec warriors, enraged by the death of their leader, attacked hundreds of Spanish troops, who were too weighed down by gold and jewels to put up a fight or escape, and many ended up falling into nearby Lake Texcoco, along with their booty.

The haul is estimated to be worth almost half the wealth ever plundered in Spanish South America. Lost items include a life-sized alligator head in solid gold, hundreds of solid gold and silver balls and pots filled to the brim with precious gemstones.

Countless searches over the years have uncovered nothing – the lake was even dredged at one point but no gold or jewels were discovered. Mexico City now sits on the lake bed, so if the treasure is lurking there, it is covered by tons upon tons of earth and concrete.

Oak Island in Nova Scotia, Canada has been the site of treasure hunts since the 18th century. A deathbed confession from a pirate who was part of William Kidd's crew in the late 18th century is thought to be the source of the treasure legend. Early settlers believed the pirate had buried treasure worth millions of pounds in a manmade sinkhole on the island called the 'Money Pit'.

In 1799, a settler called Daniel McGinnis carried out the first dig. He found a series of mysterious symbols, which when deciphered read “Forty feet below, two million pounds lie buried”. Before he could dig deeper, the possibly booby-trapped hole filled with water and the dig was called off. A group called the Onslow Company conducted another search in the early 19th century, and explorations have continued to the present day.

Famous Oak Island treasure hunters have included Hollywood star John Wayne and heir Vincent Astor. Some people believe the treasure consists of Shakespeare's lost folios and jewels that once belonged to Queen Marie Antoinette of France. Oak Island has even been put forward as a possible resting place of the Ark of the Covenant and Holy Grail.

Spookily enough, an oft-quoted prophesy states that seven people must die before the treasure of Oak Island is revealed. Six people have lost their lives searching for the treasure, victims of possible booby traps, so it could be a case of six down, one to go, as macabre as it sounds.

One of the world's most sought-after treasures, the Treasure of Lima was stolen by English trader William Thompson in 1820, after he was hired to transport the massive haul of gold, silver and jewels from Peru to Mexico.

Thompson is believed to have squirreled away the stash of booty on Cocos Island, which is located off the coast of Costa Rica. Over the years, hundreds of treasure hunters have descended on the island in search of the treasure, including US President Franklin D. Roosevelt, Hollywood actor Errol Flynn and gangster Bugsy Siegel.

An inventory of the treasure lists 113 gold religious statues, including a life-size statue of the Virgin Mary, 273 swords with jeweled hilts, 200 chests of jewels, 1,000 diamonds, solid gold crowns, 150 chalices and hundreds of gold and silver bars. All in all, the Treasure of Lima is estimated to be worth more than $200 million (£165m) in today's money.

Despite the many searches, the Treasure of Lima remains lost. Now a UNESCO World Heritage Site, the island is protected and treasure hunters require permission to explore the area, which can take up to two years to arrange.

Local rumor has it that a Nazi train loaded with hundreds of tons of pillaged gold, precious jewelry, works of art and valuable weapons was buried in the notorious Project Riese complex of tunnels, under the Owl Mountains near Walbrzych in Poland (pictured), in January 1945, as World War II was coming to an end. The stash, if it exists, would be worth billions of dollars in today's money.

The Nazis allegedly drove the train deep within the mountain complex to prevent Allied troops getting their hands on the treasures. The rumor first caught the attention of the Communist authorities in Poland after the war, who ordered the military to search the site a number of times, without success.

Interest peaked again in 2015 when treasure hunters Piotr Koper and Andreas Richter mounted a major search with the assistance of the Polish Army, following a deathbed confession they had obtained indicating the precise location of the train. The plan was leaked to the press and the world's media descended on Walbrzych to report on the search.

The location was excavated in August 2016, but nothing was found apart from dirt. All was not lost however as the local people received a different sort of windfall courtesy of the search: the intense global media interest has helped boost tourism revenues in the region by a bumper $200 million (£164m).

Dubbed 'Nazi's El Dorado', Lake Toplitz in Austria was used as a naval testing station during World War II. It is believed a hoard of looted gold and other treasures contained in metal boxes was dumped in the Alpine lake towards the end of the conflict, along with £100 million in counterfeit Sterling banknotes.

Once the war was over, the search for the lake's hidden treasures began. Tragically, an American navy diver drowned in 1947 looking for the boxes. In 1957, a German salvage team uncovered a massive stash of forged banknotes and a printing press, but no gold or precious treasures.

By the early 60s, the lake had become a magnet for treasure hunters, who risked their lives in a bid to find the alleged haul. A health and safety nightmare, the death of another diver in 1963 prompted the Austrian government to severely restrict further explorations.

The Austrian authorities have permitted several heavily regulated explorations over the years but the last major search in 2006 uncovered nothing of value. Despite that, in 2014, the nephew of Ernst Kaltenbrunner (pictured), the Nazi general who supposedly oversaw the dumping of the boxes, confirmed that they actually do contain gold and other treasures. Lurking somewhere in the lake, they are still waiting to be discovered.