In the marketplace (Stændertorvet), south of the Roskilde Royal Mansion and in the center of town, you'll find the Town Hall, built around 1880 in Gothic style and designed by the architect O. Momme.
The imposing tower dates to around 1500 and was originally the tower of St. Laurence's Church, the ruins of which can still be visited in a small museum beneath the market square.
Only one section of the church, dating from about 1125, has been excavated. To appreciate the full size of the original church, look for its outline in the pavement of the Stændertorvet.