For the ultimate girly-girl fantasy, try Mermaid Swimming School. You really do get to wear a mermaid tail (or monofin). It’s a great core and lower back workout that forces you to use your muscles in a totally new way — a little like weightless belly dancing.

Then there are the water exercises that simply move your typical gym machines underwater. Aqua cycling is a kinder, gentler spin class that won’t kill your knees but still burns mega calories — up to 750 an hour. The underwater treadmill is ideal for injured runners who don’t want to get out of shape while they heal. This is not to be confused with aqua jogging, which involves wearing a flotation device around your waist while mimicking the movement of running without touching the ground. Water resistance on all sides means underwater running and walking work more of your leg muscles than the same activities on land.