Strömsborg is a tiny circular island in central Stockholm, part of the Gamla Stan district. The name Strömsborg is derived from the Stockholm merchant Berge Olofson Ström (1688-1762), who bought the uninhabited island in 1740 and built a castle-like house on it. Previously, the island was called Stenkär.
Sandwiched between two bridges, the Centralbron and the Vasabron, the island can today only be reached via a branch in the middle of the Vasabron. The small palace on the island was built in 1895-97 and received its present form in 1929-30 by the architect Ragnar Östberg. The house houses offices of the international organization IDEA and the Council of the Baltic Sea States.