Explorers discovered the odd-shaped object on the ocean bed of the Baltic Sea in June 2011. Dubbed the Baltic Sea Anomaly, the object is a 70-metre long (210 feet) strangely-shaped feature that showed up on sonar laying 100 metres (300 feet) beneath the waves. Theories as to what the Anomaly could be have ranged from the interesting to the outrageous, with some claiming it could be part of fleet of crashed UFOs on ocean floor.
Others have claimed it could be the remains of a sunken city lost to the waves years ago.
However, some conspiracy theorists are now claiming the odd anomaly on the Baltic Sea floor is actually an underwater bunker used in the Second World War.
Conspiracy theorist website Time Loops said: “My first impression looking at the Baltic Sea Anomaly is that it resembles a 19th or 20th-century bunker and we are looking at the underside of the ceiling. It is a structure similar to the ones used during the two world wars.
“At least four key features of the main object resemble similar features found on bunkers located all over Europe.
“The corridors and rooms are the spaces in the concrete and when the two objects fit together the height of each room would be the sum of the space left out.
“The sizes of the rooms and corridors are not uncommon for bunkers and seaside fortifications.”
Despite adamants from conspiracy theorists that the Baltic Sea Anomaly is not natural, scientists state it is actually a glacial deposit formed in the Ice Age.
Volker Brüchert, an associate professor of geology at Stockholm University, said: “I was surprised when I researched the material I found a great black stone that could be a volcanic rock.
“My hypothesis is that this object, this structure was formed during the Ice Age many thousands of years ago.
“Because the whole northern Baltic region is so heavily influenced by glacial thawing processes, both the feature and the rock samples are likely to have formed in connection with glacial and postglacial processes.”