The Olsker church, built in the 12th century, is the highest of Bornholm's four round churches. The defensive architecture of this church has been carefully designed, with extremely narrow stairs to access the upper floors, preventing intruders from capturing the structure. Restorations were carried out in 1934 and 2004.
The Ny Church, built between 1150 and 1250, is the youngest of Bornholm's round churches. Like the other churches on the island, it was designed as a typical fortified structure with a wooden roof for defense.
The Nylars church, built around 1165, is considered to be the best preserved of Bornholm's four round churches. Its upper floors were used as shelter for villagers and defence, and outside, the reinforced wall can still be seen. In 1882, the interior of the church was renovated.