Uncover a hidden side to the city's history from beneath, exploring what was originally the city's 12th-century moat, later covered over to make sewers. Call ahead to find the day's departure times for 15-minute boat rides or 90-minute guided walks with information provided by tablet.
For the latter, waterproof boots and protective suits are provided: you'll emerge on Keistraat after plodding some 2km.
