"In RKAS' opinion, selling the complex into private hands is the most realistic and swiftest of the options available today for getting the complex of buildings, which has been standing idle for years, into order and taking it into use as a part of the public urban space," Timo Aarma, development director at RKAS, said in a press release.

"Imposing a new detailed plan seeking a multipurpose function is the first step toward putting this historic complex of buildings in order," Aarmaa said.

According to Aarma, the first step toward getting the historic building complex in order would be to implement a new detailed plan for its multipurpose functioning. "The participation of private capital in developing the Patarei complex is necessary in order to bring in both additional resources as well as a new vision and ideas," he added.

The detailed plan being processed for the 3.6-hectare property sandwiched between Kalaranna Street and the Baltic Sea calls for the renovation of the heritage-protected Patarei Sea Fortress and finding contemporary uses for it. The plan also provides for the possibility of erecting residential buildings up to five stories in height next to the fortress building.

RKAS estimated that renovation and upkeep of the complex would cost approximately 150 million euros over a 30-year period, with the necessary initial investment falling in the 60-85 million euro range and upkeep costs running approximately three million euros per year.

Patarei Sea Fortress-Prison, which was completed in 1840, was built on the order of Russian Emperor Nicholas I. Originally intended for use as a sea fortress, the complex was used as a barracks until the collapse of the Russian Empire. From 1920 until 2002, it was used as a prison by various regimes, and the main part of the complex was declared a cultural monument of the Republic of Estonia in May 1997.

The complex was closed to the public in October of this year.