Walking, Key West
When my son went to Key West on a Boy Scout trip on a boat, he said "We had to walk everywhere - it was too expensive to ride the Conch Train"
Key West is actually a very walkable place, especially in an around the customs house
The whole northeast side of Key West has this lovely sidewalk along the seafront. You can walk or jog or bike or rollerblade, or whatever non-motorized method that you wish to use for several miles right along the beach. The second picture also shows the East Martello tower which is a museum for which there is an entry fee.
Key West is very walkable. The tourist areas are located mostly on Duval and Whitehead Streets which are parallel to each other and don't take long to walk from end to end.
Walking is really the best way to see Key West, it's a compact town, but bicycles and mopeds are quite popular especially for sites outside the town center. Oldtown Trolley Tours are also available.