Anyone can places cache. It doesn't have to contain anything just needs to meet certain criteria such as not containing food if placed in a national park. I use Geocaching for three things. Running or mountain biking as caches tend to be in a series over a number of miles. Visiting areas I wouldn't normally visit and photography. Geocaching is great when on holiday as it takes you off the beaten track. When I was last in Canada I was chased by a bear cub.!
There are several types of caches, virtuals are when it is not physically possible to place a cache because of restrictions imposed by the landowner or climate. You just need to demonstrate you have found the given coordinates.
Virtual cache on top of Sulphur Mountain, Banff Canada.
Photo taken after finding Small cache found half way up a waterfall
Sounds nerdy I know but on the physical activity front it has helped me shift 3 stone I put on since I stopped smoking and helps me maintain an interest in Photography.
There is something like 2m active caches globally and 5m active geocachers so it's not just me being a nerd