You'll be more relaxed than ever before in Iceland's Blue Lagoon. A geothermal spa, this 5,000-square-meter lagoon holds six million liters of bright blue seawater atop a sand-like base (made of skin-softening minerals). Icelanders take advantage of nature's hot tub even in the winter, as the water is heated to around 100 degrees. In fact, one of the best times to visit the Blue Lagoon is during a light snowfall, as the contrast between the cold air and the heated water can't be beat.

Squeamish about sharing a bath with thousands of strangers? The Lagoon is actually quite clean, as the water is completely replaced every two days. In fact, the Blue Lagoon holds a Blue Flag (a recognition usually given to beaches) for water cleanliness.

The Lagoon is supposed to have healing medicinal properties for everything from skin disease to muscle pain. We can't verify the health benefits, but we can tell you that the water and complimentary mud masks will leave your skin softer than ever.

Where is it? In Iceland, about eight miles from Keflavik International Airport.

Where to stay? For ease of access, you can't beat the Blue Lagoon Clinic Hotel. Just a five-minute walk from the Lagoon, rooms feature amazing views of the nearby lava fields. Best of all, the room rates, which start around $145 for a single, include admission to the Lagoon—a $40 value.

What else should I know? Numerous tour companies run bus trips to the Blue Lagoon, but you're really much better doing it on your own, as it's easy to get to, and pretty self-explanatory when you get there.

Who's it for? Anyone who needs to relax, spa-lovers, and beauty fiends.