Two of the Top Attractions when visiting Puerto Rico are Arecibo Observatory and Rio Camuy Caves.
Arecibo Observatory: Located 10 miles outside the city of Arecibo is an astronomical observatory, which houses one of the world’s most powerful radar-radio telescopes, and the largest single-unit radio telescope in the world. When I think of ET trying to phone home, this place comes to mind. The antenna can be moved in any direction, making it possible to track a celestial object in different regions of the sky. It collects radio astronomy, terrestrial aeronomy, and planetary radar data for scientists around the world. The telescope was featured in the movies GoldenEye (1995) and Contact (1997).
Rio Camuy Caves (Spanish: Parque de las Carvernas de Rio Camuy): It’s the third largest cave system in the world and probably one of best caves that I’ve been too. It’s best to arrive early, before 9:30 a.m., to avoid the crowds. Once you park you board a trolley that will take you down through the park to the cave entrance. The tour takes about 1.5 hours. The only restrooms are located at the main entrance, so plan accordingly. The caves are cool, so you may want to bring a jacket. The walkway is wet, and some parts slippery, so be sure to wear sneakers or shoes with good traction, and use the handrails as suggested. People with medical conditions like asthma shouldn’t go in. You are allowed take all the pictures you want. The guides will point out the best places to get good shots.
You can see both of these attractions in the same day. It’s a great day trip from San Juan.