The church ruins in Maridalen valley are one of few memories in Oslo from the Middle Ages.
The Church of Margareta was built around the year 1250 AD. It was a small, single-nave church with choir, dedicated to St. Margareta. The medieval church was partly excavated and restored in 1934, and is beautifully situated at Kirkeby in the north end of the lake Maridalsvannet.

The historical play "Maridalsspillet" is performed in the ruins every year (late summer).