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.
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Photo taken after finding Small cache found half way up a waterfall
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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