This unrefined seven-storey tower is the most significant remnant of the former St-Trudo abbey church, dating partly from the 11th century but left as a shell following a 1975 fire. Climb the tower's shell to a rough metal viewing platform to survey the city.
To gain access you'll need a code that comes with the TrudoPas, which also gets you into the crypt of the abbey church, otherwise demolished in 1798 (metal poles show the height of the original internal pillars).
Note that lone visitors are not permitted to climb the tower – there must be at least two people at once.