Patarei Sea Fortress was established between 1828–1840 by order of Emperor Nicholas I as part of the Russian Empire's Baltic Sea fortification system, initially as an artillery battery and sea fortress. The building was later adapted into barracks and, from 1919 until 2005, it was used as a prison.

After the property's ownership changed in 2019, an invitational architectural competition was organized in 2020 in cooperation with RKAS (State Real Estate Ltd) and the city of Tallinn. Its goal was to find a solution for covering the distinct inner courtyards and to create high-quality public space and a new architectural identity for the surrounding urban environment.

The architectural competition was won by the entry 'Taevakaar' (Sky Arch), authored by HGA in collaboration with Väli landscape architects. The project supports the functional and energetic transformation of the Patarei Sea Fortress, adding a contemporary layer and a strong architectural identity to the historic building. The Gorge and Lunette courtyards will be reconnected. The historic, strictly geometric structure of the building is balanced with smooth, curved roof forms.

The roof of the Lunette courtyard is supported by three interconnected arches, on which a glass surface rests with the help of glulam or steel beams. The supporting structure of the Gorge courtyard's roof consists of specially shaped beams or spatial trusses, emphasizing architectural distinctiveness and openness.

Authors of the competition entry: Marianna Zvereva, Andres Ristov, Andrea Ainjärv, Grete Liis Nagelmann, Hanno Grossschmidt, Tomomi Hayashi / HGA + Kadi Nigul, Kristian Nigul, and Kadri Uusen / Väli landscape architects