San Juan is a spirited modern city with high-rise beach strips and a justly famous colonial core. Founded in the 16th century, it's the second-oldest city in the Americas; today it's the engine of the island's economic and political life and the cultural beachhead for US influence in the Caribbean.
Many Caribbean adventurers never make it past Puerto Rico's seductive capital: there's a lot to be said for being able to lay a towel down on a pristine white Caribbean beach while having the culture and quaintness of a historic city and the convenience of a modern metropolis just minutes away.
Nearly half a billion dollars have been spent preserving the colonial core of Puerto Rico's second city, and it's not only architecture buffs who declare the money well spent. The heart of Ponce dates from the late 17th century and has been declared a national treasure.
It consists of plazas and churches and highly decorative colonial homes, some glorious fountains and what may well be the funkiest fire station in the world. One of the reasons Ponce is so easy on the eye is that an early city regulation required that street corners be chamfered (curved).
This jagged karst region in the northeast of Puerto Rico is littered with sinkholes and surreal limestone formations, making it prime spelunking territory. Over 200 caves have been discovered in the region, some capable of swallowing skyscrapers.
The Camuy River is one of the largest subterranean rivers in the world. Experienced cavers can get dirty and wet by climbing, scrambling, abseiling and swimming through the underground river system, but some experience is required to contemplate entering this dangerous terrain.