[Sundae]

Limey has it. It's not all interesting, and some of them are still filthy, but you see a side to cities you wouldn't see otherwise.

Friends of mine in Leicester ran two boats owned by the Narrow Boats Trust (do NOT call a narrow boat a barge! Glare of death!) They went on coal runs to and from London every year, so they could be classified as working boats. London's canals were a revelation to me - I thought I knew the city. But I hadn't seen its waterworks.

I went to a narrow boat event in Maida Vale and enjoyed it immensely.
I'm too claustrophobic to choose it as a holiday though.