The cathedral's nave was torn down in 1674 by North Sea Winds (remember Cyril last year and it will not sound improbable). Only the tower and the transept remained. So today there is a big gap between the tower and what passes for the cathedral in these days. Filled with trees, in the summer it must be a lovely place to walk, enjoying the surroundings. This winter it is an eerie landscape of green tree-trunks (a result of the moss that covers them), looking strikingly otherworldly against the earthly and reddish hues of the chancel.
You can go under the tower to the other side of it through a small tunnel at the base. I did not have the time to climb the stairs but will do in the future!
Walking away from the tower, the view from the canal is sublime... actually the tower serves as orientation so that one does not get lost in the narrow streets of the old city.