Ribe Cathedral — formally the Church of Our Lady — is the oldest cathedral in Denmark and the country's only five-aisled church. The current building was begun around 1150 in southern Romanesque style, on the site of a wooden church founded around 860 by the Benedictine missionary Ansgar; the western towers, the apsidal east end and the lantern at the crossing all date from the medieval campaign.
The interior is bright and remarkably airy for a building this old. The most striking modern feature is the cycle of stained-glass windows, mosaics and frescoes in the apse and choir by the Cobra-movement artist Carl-Henning Pedersen, completed in 1987 after years of local controversy. Climb the Borgertårnet (Commoner's Tower) — 52 metres and 248 steps — for a panoramic view across the marshes to the Wadden Sea, 30 km off.