Lago Enriquillo was a must-see couple of years back. The crocodile watching was my favorite, when the lake was still with lower water levels and boats operational. They had a curative sulfur spa which has now been completely ruined by growing water levels in the Lake. Emergency sessions are being held because the Lake is growing uncontrollably.
Also Polo Magnetico by Cabral is a nice hangout spot for observing optical illusion where you can have a soda can roll uphills, or even a car seemingly go uphills in neutral.