Maurice X.
There are many different types of exercises some traditional and some less traditional.
Some traditional exercises are: Running, walking, lifting weights, stair climber, swimming (my favorite), cycling, and different types of gym classes at your local gym.
Other non traditional exercises enclude: snowboarding, mountain biking, hiking, backpacking, scuba diving, snorkeling, biking instead of driving, surfing, and so much more.
When it comes to walking I generally do 10 min to 2 hours. I always go with my girlfriend (we live together) which making going for a walk easy. I would say if your walking for an exercise do it for 25+ and walk with someone: family, loved one, dog, or just a friend. This will make if it more fun and easyer to keep it up in the future.