Every so often someone asks about visiting Venice with a walking disability or as a wheelchair user. The latest issue of International Travel News has an item about a book that might be helpful. "Venice: Easy Sightseeing: A Guide for Casual Walkers, Seniors and Wheelchair Riders". (ISBN1419698745) $15.99
ITN says it contains 14 sightseeing routes, each a 3 to 5 minute walk from a boat dock, plus maps & descriptions of wheelchair-accessible paths, elevators & bathrooms.