Cartagena (pronounced cart-a-hay-nya) has a brand new catamaran service (January 2012) from the end of the dock to the "old town," with its narrow streets and Bouliva Plaza with its free gold museum. The trip costs $5 per person round-trip and takes about 15 minutes each way. An excellent independent excursion.
Puntarenas, Costa Rica, has a mile or so of shops and stands, the people are extremely friendly, and there are actually some bargains to be had. (Note the beautiful rosewood bowls and boxes!) The dock is perhaps a hundred yards long, and the stroll along the main street is interesting.