The legs are the longest part of the body, so they need to be kept in good shape.
There are plenty of exercises designed to improve strength and flexibility.
So here are a few to get you started.
A simple exercise that works the whole leg and your backside
A good endurance exercise for working the heart and circulatory system
Tone and build your upper thighs and backside
Another good machine for those who aren't keen on the exercise bike or treadmill