Trelleborgen is a 9th-century Viking ring fortress, discovered in 1988 off Bryggaregatan (just west of the town centre). A quarter of the palisaded fort and a wooden gateway have been recreated, as has a Viking farmhouse and a medieval house built within the walls. A small museum showcases finds from the archaeological digs, including Viking jewellery, grooming implements and a 10th-century skull illustrating the ancient trend of teeth filing.
The fortress is built to the same pattern as Danish fortresses of the same era, showing the centralised power of Harald Bluetooth at work.