For many travelers, a hotel's most important attribute is the guest room. How big is it? Does it have great views? Who designed it? Sure. But count us as big fans of an extravagant pool. We've all seen those Instagrams of bikiniclad cliques wading in an infinity pool, umbrella drinks in hand. That's nice. But what if the pool was in a Viennese bank vault and made of gilded bricks? Or wrapped around a sandstone boulder under the desert stars in Utah? Bright sun and ocean vistas are great, but a gamechanging pool can take your breath away. Here, a selection of the most exciting pools in the world.