Today the Trelleborg fortress is part of the National Museum of Denmark, and consists of a museum, a visitors' centre and the Trelletorp Viking village with a longhouse and other Viking-era buildings that have been reconstructed using authentic materials and techniques.
Unlike the other ring fortresses, the Trelleborg at Slagelse was extended with a sort of bailey.
In its day the Trelleborg fortress lied on a peninsula jutting into the swampy area between two rivers.
Like the other Viking ring fortresses discovered so far (seven as per 2014), the Trelleborg at Slagelse was designed as an exact circle: two roads facing the compass points divided the internal part in exactly four same size quarters and led to the four gates with two always opposite to each other.
In each of the quarters stood four longhouses arranged in a square.
The swamp was connected to the "Great Belt" (a strait between the islands of Zealand and Funen) by a lake that could be navigated by Viking ships.