San Carlos is less a tourist destination and more a place to wait for your ship, or panga (small motorboat), to come in, but there is beauty here – particularly on the grounds of Centro Cultural Jose Coronel Urtecho, which is set within the crumbling walls of Fortaleza de San Carlos. It’s no El Castillo, but it was built in 1724 and has amazing lake and Río San Juan views. There’s another old Spanish observation post, with cannons, at the end of the malecón.