Looming atop a marlstone hill with commanding views of the Maas, the five-sided Fort Sint Pieter formed the city's southern defence and is linked to a network of underground tunnels. It's been fully restored to its original 1701 appearance. Visit is by guided tour only, which can be combined with a tunnel tour. Purchase tickets at the visitor centre below the fort. It's a 2km walk south of Maastricht, or take bus No 7 and get off at 'Mergelweg'.
Three nature walks begin from here, each marked by colour-coded posts. The fort is also the southernmost point of the Pieterpad, one of the Netherlands' most popular long-distance hikes, extending 492km to PIetersburen in Groningen province.