Four of Denmark's seven medieval round churches (rundkirke) are located on Bornholm. Originally built around 1150, these uniquely round churches were used as places of worship, storage for passing ships, and fortresses to protect against attack during the middle ages. There are rumors that some of the churches were associated with the Knights Templar.
The round churches are striking whitewashed buildings, with upper stories designed to double as shooting galleries against enemy attack. Originally, they had flat roofs built to better support fortification against invading pirates. The largest round church is in Østerlars, with others found in the villages of Olsker, Nylars and Nyker.
All four churches are still used for Sunday services and are open to the public from Monday to Saturday.