Add this to your list of things you never knew existed but, now that you do, you now desperately need: a visit to NEMO33, the deepest pool on Earth.
NEMO33 contains over 2.5-million liters of chlorine-free, filtered spring water that's been heated to 86°F. Much of the pool is between 5- and 10-meters deep, a number of "caves," ripe for exploring, positioned at the 10-meter depth.
There's even a restaurant where you can observe divers while enjoying a meal or a cocktail. But the pièce de résistance is undoubtedly the facility's 34.5-meter-deep diving pit, the deepest indoor diving well on Earth:
The facility looks like it would be an absolute blast to explore. A Google image search for nemo33 turns up pages of underwater photographs that make the pool look a bit like an abandoned apartment complex, long overrun by floodwaters. Imagine what it would be like if you could play laser tag in there. Is that a thing? Underwater-environment laser tag? If not, somebody should get on that.
h/t Ben Lillie