There are several tour companies that offer this package. My recommendation? Call Countryside Tours. Several hotels also offer the tour, so you might want to check with the front desk before making a call.
Of course, you can also opt to drive yourself. Most of the major car rental companiesare represented on the island. The observatory is about 1.5 hours west of San Juan. It's mostly a straight shot on Route 22 until you reach the town of Arecibo. Then head south on Route 10 for about 20 miles and then follow the signs to the observatory. From here, take Route 129 southwest for roughly 12 miles to the entrance of the Camuy Caves.
So, why are you making this trip? Simply put, you're visiting two sites that are unique in the world. The Arecibo Telescope is the world's largest radio telescope, a remarkable feat of engineering, and the site of the climactic last scene in the Bond movie "GoldenEye" (for all the 007 fans).
The Camuy Caves are among the largest subterranean cave systems in the world, and the only one of its size to boast an underground river. Visitors travel in open-air trolleys and then take a 45-minute walk through the caves, admiring the stalactites, stalagmites, and natural vegetation that flourishes in the system.
This is an all-day trip. Fortunately, you'll be rewarded in the evening with a culinary excursion into Puerto Rican fine dining. After a rest in your hotel, head to Ajili Mójili and enjoy some of the best local cuisine on the island.
Day 5 will be another journey into Puerto Rico's verdant interior.