Scuba diving.
Not everyone would have the opportunity to practice it, but I really recommend it. I consider it the ultimate hobby.
Don't miss the chance to do it at least once, when you're on vacation, and if you like it, it can be a lifelong hobby.
You know, one lifetime is not enough to visit everything that is on land, which occupies 29% of the earth's surface, but how much time do we need to visit everything that's underwater? I wouldn't want to die until I see at least a part of what is hidden under the water.
On the other hand, scuba diving is neither the cheapest hobby in the world, nor the most expensive, you can see here
all expenses related to scuba diving. But believe me, it's worth every penny for what you'll see and what you'll feel when being at least 30 meters underwater.