Exercise without the gym

I'm 15, a guy and haven't exercised in like a month or something I'm not fat just skinny. I was into it for a while, but stopped and then couldn't get back into it. I always wanted people to give me advice on what to do to maintain a regular exercise plan. Can anyone give my some suggestions on how to get fit without having to go to the gym?
Thanks a lot.

It depends on that where you live. Kayaking is a very good sport (it is my favorite) , hill climbing also (it is may second activity), if you can afford horse riding that is excellent, or swimming also gives you good condition. If you cannot do any of these activity then put a good music on and try to make eurhythmics on that in your room at least for an hour, after or before of this you may make one or half on hour jogging. You will be in good condition.