In the the late 1800s an eccentric con-artist millionaire in England built a mansion with one of the most unique features in the world. Under a man-made lake, he had an underground billiards room made. This room is enclosed in thick glass windows that filter the light from above and cause an eerie glow about it. The whole underwater system was set up to entertain party guests who would smoke, enjoy a game of billiards, dance, and admire the fish that swam by out the window.
Alas, the builder of the estate was a con-artist, and after he was convicted of fraud from bad loans in the early 1900s, he took his own life. The (above ground) mansion went into disarray, but the underwater portion are still intact, but judging from the photos, it doesn’t look like it will last forever.
Unfortunately, this picture with someone in it gives the room some perspective, and shows that it’s not really that large.
In case you’re wondering what it looks like from above ground, here it is at night, illuminated from below with the statue of Neptune showing it’s peak.