Riddarholmen ("The Knights' Islet") is a small islet, part of Gamla Stan, the old town.
Its main landmark is the church Riddarholmskyrkan, the burial church of the Swedish monarchs. It is one of the oldest buildings in Stockholm, some parts of it date to the late 13th century, when it was built as a greyfriars monastery.
After the Protestant Reformation, the monastery was closed and the building transformed into a Protestant church. A spire designed by Willem Boy was added during the reign of John II, but it was destroyed by a stroke of lightning on July 28, 1835 after which it was replaced with the present cast iron spire.