Venice
Certainly one of the unique cities on the planet; an entire city built on the water. No roads, no cars, busses, motorcycles, bicycles, no motor vehicles of any kind, just boats and walking. The police, ambulances and fire vehicles are all boats. Excellent mass transit; large bus/boats ("vaporeti") run regular shedules cheaply and reliably, and are generally very crowded. Get off your flight at Marco Polo airport and hop on a taxi boat and go straight to your hotel. An amazing place...narrow sidewalks lead to large piazzas where kids are playing soccer, and canals everywhere.
