The centre of Huy is overshadowed by this indomitable stone fortress, an oppressively dour triangular structure, built by the Dutch between 1818 and 1823. Its use by German forces in WWII as an interrogation centre for 7000 prisoners is the focus of an extensive memorial-museum in its cavernous bowels. Access to the site is via a footpath zigzagging up from the riverside beyond the church or by cable car (April to October).
From the grassy roof (but not the access path) there's a great panorama looking down across the church towards the brooding cooling towers of the Tihange Nuclear Power Station.