Venice
Venice is one of the most interesting and lovely places in the world. This sanctuary on a lagoon is virtually the same as it was six hundred years ago, which adds to the fascinating character. Venice has decayed since its heyday and is heavily touristed (there are slightly more tourists than residents), but the romantic charm remains.
Venice is the world's only pedestrian city, is easily walkable, and the absence of cars makes it a particularly pleasant experience. Walking and standing all day can be exhausting too so acclimatise yourself. The Rialtine islands - the 'main' part of Venice - are small enough to walk from one end to the other in about an hour.
If you want to get around a bit more quickly, there are numerous vaporetti (water buses) and water taxis. The vaporetti are generally the best way to get around, even if the service route map changes frequently. If you are going to be in Venice for a few days visiting, it is a lot cheaper to get the vaporetti than to get private water taxis. If you want to have a romantic ride along the canals, take a gondola ride.
The city is not that big, and you can walk from one end to the other in a few hours. But it would take months for a fit person to discover every path in the city. Along the way you will discover marvelous art, superb architecture and breathtaking urban landscaping. Exploring the city randomly by walking is well worth it but also be prepared to get lost easily! Signs all over the city indicate the direction to the main attractions, "Rialto" and "San Marco", as well as the way back to the train station ("ferrovia") and the bus terminal ("Piazzale Roma"). These signs make it easy to have the "get lost experience" even as a one-day tourist.