The Observatorio Astronómico on the campus of the University of Puerto Rico at Humacao is open to the public at 7:30 p.m. the second Thursday of each month during the academic year for viewings of the planets and stars; phone (787) 850-9344 or (787) 850-0000.
Just offshore is the island of Cayo Santiago, a field station of the Caribbean Primate Research Center. More than 400 Rhesus monkeys were released here in 1938, and their descendants roam the island today. Access is restricted, but diving and fishing charters provide an offshore glimpse of the colony.