Colonia is a great place to go for a quiet, relaxing day trip away from BA. There's not much to see other than the colonial town itself (which is beautiful), the river coast, and just walk or relax. We go there from time to time to have lunch, enjoy the afternoon, and come back the same day. If you want more than that, take your driver's license and rent a golf car (or scooter) to drive around. You can go visit the old bull-fighting stadium ruins and ride along the coble stone streets. It can be fun. Golf car rentals are right outside the ferry terminal.