Puerto Rico offers the perfect balance between tranquil retreat and rum-soaked nightlife. The Spanish colonial buildings of San Juan give a beautiful backdrop for a day of shopping and sightseeing. Hike the massive El Yunque rainforest to see waterfalls, stone towers, and colorful Puerto Rican wildlife. As far as beaches go, it doesn’t get better than the sands of Isla de Vieques—particularly Mosquito Bay, where by moonlight the water glows blue-green thanks to bioluminescent microorganisms.