Best known for its cobbled colonial streets and old forts, Puerto Rico’s capital city has transformed into a major metropolis since Juan Ponce de León first landed here in 1508. The second-oldest European settlement in the Americas packs plenty of historical and cultural appeal and doubles as the gateway to the rest of this US territory in the Caribbean. Well over 3 million visitors come to Puerto Rico each year for sandy beaches, mangrove forests, colorful coral reefs, and the only tropical rain forest in the US. Here are our top picks for activities that you shouldn’t miss while on the island.