Belize’s entire Caribbean coast is hugged by its namesake barrier reef, the second-largest on the planet. You can explore this UNESCO World Heritage Site when your Holland America Line ship drops anchor in Belize City; hop a boat to tiny Caye Caulker for up-close encounters with stingrays and harmless nurse sharks. Grab a tube for a subterranean float through Belize’s vast cave systems, zipline through the jungle canopy, or visit the ancient Mayan centers of Xunantunich, Altun Ha, and Lamanai.