There are three things I really like to do for fun when it comes to fitness/athletics/outdoorsy type stuff. One of them I only just started researching and doing. The other two I have practiced and researched for quite some time, literally a couple of years. These are weight training, martial arts, and parkour/free running. All three quite fun, very beneficial if done correctly and safely, and all of them yeild the ability to do things that make people say, "What the heck?" These activities are all quite entertaining. Let me explain them.
Weight training is the adding of resistance to certain body movements to force an adaptation. If done with proper form, at a reasonable difficulty, and only 1 to 3 times a week weight training can yield ridiculously awesome results when it comes to over all fitness. The most important exercises are deadlift, squat, dips, chins, rows, shoulder press, and heavy ab work. Adding resistance over time will cause increases in strength which usually mean increases in muscle mass, which means that eating the same amount of calories as always will result in fatloss. Rock On!!!
Martial Arts are just what they sound like war arts. They are more of a science than an art, in that you learn to most effective paths of movement for your body to the most vulerable spots on your opponents body. But the training itself is art like often times, and the ability to be creative about the accomplishing of the scientific goals(properly attacking opponent or defending from opponent) it most assuredly art. Much like Nikola Tesla's inventions could be considered artistic just because of the creativity he put into his research to discover new things.
Parkour/Free Running is very hard to describe, but it's basically running in urban areas and jumping all over obstacles. It could range from doing a flip over a pool of water in front of a corporate building, to running up a wall and jumping onto a ledge to get on top of a two story apartment complex. It's pretty cool. This is a horrible definition, but maybe you'll get the idea. It's called free running because it is free, you don't allow obstacles to stop you. It's like skateboarding with no board, and less restrictions, because I don't need ramps, just feet.
These are great fun, and good physical/mental disciplines. I really enjoy doing them so far, Lord willing I will be able to do them for many years.