Spring Hill, Florida. The mermaid theatre is the original 1947 underwater amphitheatre; performers still pass the audition by holding their breath through a 120-foot dive and treading water for ten unbroken minutes. Outside the show: a riverboat to spot manatees, a wildlife enclosure with a three-legged tortoise named Tripod, a roped swimming area in the spring itself. Admission $13. The kind of place that’s only memorable because it should not still exist.