The old town of Tønder is compact, extremely well preserved, and contains one of the best collections of 17th and 18th-century merchant architecture in southern Jutland. The gabled houses that line Storegade, Vestergade, and the streets around the old market square were built by prosperous lace merchants at the peak of Tønder's commercial success, and the town has managed to protect them from the worst of 20th-century redevelopment.
Walking the old town takes about an hour at a comfortable pace. The Tønder Watermill (Tønder Vandmølle) is worth seeking out — one of the few surviving water-powered mills in the region. The main church, Kristkirken, has a fine carved baroque interior. The streets are quiet enough that you can stop and look at the facades in detail without fighting foot traffic.