The church hall is located on the third floor of the Rooster Tower. It was used by the townspeople until Hämeenlinna received city rights from Peter Brahe in 1639, and a separate church was built north of the castle in 1666.

The Somero altarpiece on the south-eastern wall tells the story of the faith of the Reformation era and Finland's international connections. As an object, it is unique in Finland. The central motif of the altarpiece, which was probably made in Northern Germany at the beginning of the 16th century, is the so-called Rosary Mary, surrounded by a cloud halo and angels carrying the heart and wounds of Christ.

The hall displays also one of the oldest crucifixes from the National Museum of Finland’s collections, originally from Vanaja Church. The adjacent room served as the church’s sacristy and contains four medieval church sculptures.