The spring-fed Santa Fe River goes underground in a very large slow-swirling swallet or swallow hole within O'Leno State Park, in north-central Florida. The park was built by the Civilian Conservation Corps in the 1930's. Well-preserved CCC-built structures include a dining hall, log dance hall, and a large sturdy suspension foot-bridge over the river. The camp headquarters now houses a small CCC museum. The Santa Fe River reemerges from underground about 3 miles away, in River Rise State Park.