Powerkiting: a powerful workout.

Kites are universally known like kids' stuff, good for spending some hours on the beach during a windy day.
In the world of extreme sports, kites mean those large and expensive flying object that allow kitesurfing or kitebugging.
Actually there is something in the middle of those two opposite concepts, that's usually called powerkiting.
Just imagine standing in an open space during a windy day, keeping in your hands two ropes that allow the control of a kite flying over your head. Sounds simple and relaxing, right?
Ok, now have a look at this video that I found on youtube:

I think that you can imagine that this can be a hard workout.
It will hit hard on your upper body, but also core and legs will have a decent training.
Do it for 45 minutes or so and it will let you breathless.
The best part of this type of workout is that you don't need the hi-tech kites used for kitesurfing or kitebugging. A kite between 2.5 and 4 meters (depending obviously on the power of the wind) will be enough for an exausting workout. Plus, a two-lines kite is what you need (kites used for surfing or bugging have 4 lines).
This category of kites, usually called trainers, is not very expensive: with less than 200 euros you can buy a very good one  (to make a comparison, a kite for surfing may cost 1000 euros or more), it will last a lot and will give you hours of hard training... and a lot of fun too.

Safety notes:
If the wind is strong, remember to wear a helmet and some security gear, as what you see in this video may happen:

In my experience, being pulled up in the air is quite uncommon if you don't want to (there are some manouvers for that but my advice is to avoid those tricks as the wind is always unpredictable, you will never know how long your jump will last)
It's way more common to be dragged down with your face on the ground, which isn't pleasant at all.