La Placita is a market that turns into a walking street at night -- think New Orleans' Bourbon St. Come for music and drinks, and soak up the local nightlife.
Did you know, that Puerto Rico is home to the US's ONLY rainforest ecosystem? the rainforest rises as a moat on the island's eastern coast that protects the island from hurricanes. I recommend looking for tour-guided trips to this area. Do it like a local and stop by the Kioskos in Luquillo for some tasty eats.