The Fortress of the Immaculate Conception, located in El Castillo, Río San Juan, Nicaragua, is a historic Spanish colonial fortress offering a glimpse into the region's past. Visiting the fortress generally requires a boat trip along the San Juan River. While it is possible to explore solo, a guided tour enriches the experience with historical context. The dry season (December to April) is typically the best time to visit due to more favorable weather conditions. Expect to spend a few hours at the site. Cost can vary based on transport and tour options; research and compare prices beforehand. Accessibility may be limited due to the nature of the site and transport options.