Translated as "The Sea Baths of Monte-Carlo," this spa is one of Monaco's most beloved. Salons, gyms, treatment rooms and restaurants are spread across four lavish floors, and though the spa is very discreet about its clientele, it often serves the jet-set crowd (think: Formula One and quasi-royalty). Spa treatments range from underwater massages and seaweed body wraps to anti-aging treatments and daylong pampering sessions. Visitors suggest a dip in the indoor heated pool or a soak in the outdoor Jacuzzi that overlooks the harbor. Recent travelers were pleased with their treatments, though they did note the high cost.

You'll find the spa located beside the famous Hôtel de Paris. Prices vary by treatment and/or package, but you can expect to drop a decent chunk of change on services here. For more information, visit the spa's website.