The only reason I could understand for visiting Monte Carlo is to visit this fabulous spa/resort. My wife and I went there on a recommendation from some fellow travelers. They were searching for a back massage while on the French Riveria and this was the only place they found. WHAT A LUCKY FIND! The Thermes Marins is a spa for the rich and famous. My wife and I (traveling on a tight budget) felt like paupers in the prince's castle. This spa offers many things, but their specialty is 4 'treatments'.
My wife and I received an algae wrap, hydrotherapy massage in a juccuzi, back massage with warm water and oils, and an underwater shower (standing in water with someone using a showerhead to spray you down).
While at the spa, you are given a big fluffy white terry cloth robe to lounge around in. After your treatments are finished you are welcome to use the weight and fitness center or use the pool (filled with warmed Med. Sea water). The best part was that the entire experience cost us 770FF each. So for about 110 USD, we had a phenomenal experience that we wouldn't have had in the US.
You will need to call to make a reservation a day or so ahead so they can schedule your 'treatments'. The spa is attached to the Hotel Paris if you are unable to get the phone number.