Divers believe the may have discovered a priceless chamber - often dubbed the Eighth Wonder of the World - in a shipwreck.
The jewel-studded Amber Room was built in 18th-century Prussia and installed in the Catherine Palace near Saint Petersburg, Russia.
It was dismantled by Nazi German soldiers during World War II and taken to the city of Koenigsberg.
It then disappeared - and its fate has remained a mystery ever since.
But those involved in a diving expedition in the Baltic Sea believe the long-lost room may be located in a shipwreck found last year.
The group of Polish amateur divers found the wreck of the Karlsruhe, which sank in April 1945, in 2020.
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The wreck is located at a depth of 88 metres (289 ft) and a distance of 70 kilometres (43 mi) from the Polish coastal town of Ustka.
According to expedition leader Tomek Stachura, there is "a one to two per cent chance that the room is actually in the numerous locked boxes that we saw during the last dive with robots".
Historian Piotr Michalik said: "The ship was very heavily loaded with 306 tons, two minesweepers protected it, so it could have been valuable cargo on board."
The divers will be conducting 12 dives a day from Monday and, in teams of three, will enter the wreck through an open shaft in the middle of the ship.
They will then have half an hour to examine the boxes with the help of underwater scooters before they have to surface.
A replica of the opulent Amber Room can be seen today at the Catherine Palace. It took decades to complete and was inaugurated in 2003.
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