If you've seen Michael Phelps in his swimsuit, you know swimming is a great way to get incredibly fit. The water provides natural resistance, which builds and tones muscles. Swimming also strengthens the heart, improves flexibility, works muscles that are largely ignored by other exercises, reduces stress and burns a whole lot of calories.
As terrific as swimming is for athletes of all ages, it has added benefits for senior citizens. The water supports the weight of the body, so stress on the skeleton is eliminated: no impact means no injuries. It can also ease arthritis. (The most common injury is to the shoulder, caused by overuse among competitive swimmers.) For proof, look to veteran long-distance swimmer Diana Nyad: the 61 year old is working on a record-breaking 103-mile swim from Cuba to the Florida Keys.
Yoga is one of the best ways to improve your health, all without running, jumping or lifting anything- and it makes you tangibly happier. Because there's so much room for variation (flexibility, even) in how it's practiced, yoga can be tweaked to accommodate participants of any age, and builds strength without over-stressing joints or muscles.