BRAZIL // Authorities take sustainability seriously in this watery Eden, where you can swim beneath waterfalls, dive in caves with massive underwater stalagmites, and float down rivers clear as glass beneath a pinkening tropical sky. That means popular attractions have strict visitor limits, so book ahead. Found in the landlocked state of Mato Grosso do Sul, Bonito owes its landscape to its Swiss cheese-like karst geology, where rock eaten away by eons of rainfall turns into caves and sinkholes. There are few places in the world with rivers clear enough to snorkel in. Lay on your stomach and let the current move you as tropical fish flit past your mask, while the chatter of capuchin monkeys in the trees above is dulled by the water's burble. * SEE IT! The bus from Campo Grande takes about five hours; there are limited flights. All sights must be booked ahead with tour operators.