Work on the now decrepit complex started as early as 1828, in time turning what started out as a coastal artillery site into a fortress and later on a prison.

The premises of the new museum will also accommodate a unique new international institute for the investigation of communist crimes. According to curator Martin Andreller, planning for an entirely new building would have been easier. But while Patarei prison comes with plenty of challenges, its unique location and past make it the perfect place for the institute and museum.

"International research into the fates of the countries that were occupied, of the people who suffered as a consequence of the Molotov-Ribbentrop Pact, and then making this research available to the public is a unique initiative," Andreller explains. "The sphere of influence covered by the secret protocol of the 1939 pact between the Soviet Union and Nazi Germany will be one of the focuses of the permanent exposition."

Patarei is ideally suited for the purpose: both regimes held and executed political prisoners here. One of the aims of the museum is to immortalize the memory of the victims that passed through this specific prison.

Justice Minister Urmas Reinsalu (Isamaa), who signed the agreement with RKAS on behalf of the government, has been a vocal supporter of the project. "[The project] will be the first museum to extensively deal with crimes committed by communist regimes," Mr Reinsalu was quoted as saying in a Justice Ministry press release. "This will decisively support scientific and educational work worldwide and preserve the memory [of what happened] for future generations as well."

"The centre will house an investigative centre, the museum and also an international scientific department," he added. "The message of the museum is that the evil of communist crimes can't allow to be repeated in our society."

The floor space currently allotted to the museum amounts to some 5,000 of Patarei's roughly 17,000 square meters. According to Mr Andreller, this number could still go up, which is one of the reasons why it is difficult to say what the museum will eventually cost.

The design contest for the museum was won by Japanese architect Shuhei Endo's entry in April last year, titled "Red Erosion". Impressions of Mr Endo's entry can be seen at the top of this article.