Castillo de San Marcos is an old historic Spanish located in the heart of St Augustine’s Historic District. As a result, it’s one of the top places to visit in St Augustine. This fort is a National Monument, therefore admission is free with an America the Beautiful National Parks Pass. If you don’t have a pass, admission is $15 for adults. Admission is also free during the St Augustine History Festival in May. Here are five reasons to visit Castillo de San Marcos, in no particular order: 1. Admire the Architecture of the Oldest Fort in the US The Castillo de San Marco was built by the Spaniards to defend…