Archaeologists in Sweden are seeking permission to excavate the unique wreckage of a 14th Century ship found in the heart of Stockholm's waterways.
The wreck is half-buried in the mud 10m below the surface (photo: National Maritime Museum)
Research for an underwater railway link revealed the remains of one of the oldest vessels ever found in Sweden.
Experts hope it will reveal clues about boat-building techniques and trading practices in the 1300s.
But further research will have to wait until the freezing Swedish winter comes to an end in April.
Just over 1.5 metres (5 ft) of the boat was found 10m below the surface of the Riddarfjarden bay, near the old part of the city, in September.
The rest is believed to be buried in the mud - which increases the chances of it being better preserved than if it had been found on land.
Project leader Marcus Hjulhammar, of the National Maritime Museum, said it was difficult to say exactly how much of the ship was still buried, but it could be between 10m and 20m in size.
He said he believed it was similar to a caravel type of light ship.
"I have worked on other projects underwater but this is very special, as it is in the middle of Stockholm and underwater," he told the BBC News website.
"I hope we can learn about Stockholm's history during the 14th Century, about trading, perhaps to other countries.
Pieces of leather are believed to have been used to patch a crack (photo: National Maritime Museum)
"It is very fascinating and we hope now to do more excavations in the spring."
Underwater archaeologists have already found the ship had a large crack in the worn-down hull, which had been patched up by a piece of leather - giving clues as to why the boat sank.
Sweden at the end of the 14th Century was part of the Kalmar Union that united Denmark, Norway and Sweden under a single monarch.
Stockholm was a much smaller city than today, but still the main trading centre for Sweden.
The location of the wreck means it would probably have been just outside the city at the time.
Experts hope the mud will have preserved the buried remains (photo: National Maritime Museum)
The museum hopes the city council will give its experts more time to excavate and examine the ship in the spring.
Sweden's last major underwater discovery was the 17th Century Vasa warship, which is now a tourist attraction at one of the city's museums.
Mr Hjulhammar said there were a number of options for the 14th Century wreck - including putting it on display, or simply moving it underwater and covering it up again.
"It is not always the best idea to take it up," he said.