I happen to LOVE Tennessee. Everywhere, Tennessee. However, Sweetwater Tennessee has the Craighead Caverns and found within these caverns is the Lost Sea, the largest underwater lake in the USA and the second largest in the world. It is a little freaky to imagine just how deep this lake goes when you're putting around on the surface in a little boat powered by an electric motor.
It actually has a 'false' bottom if you will. The water is lit up like a swimming pool at night and when you look over the side there is a sandy bottom and a few fish swimming around, but this bottom is actually a shelf, solidly attached to the sides of the rock all the way around except for a little space on one side that is as black as a monkey's heart. It's black because there is an opening leading to the rest of the underground lake. Divers have gone to depths of 800 feet and still not found the bottom. At least that's what we were told when we were there. Perhaps modern technology has allowed for more accurate measurement and that's how they know it's the second largest.
From their website found here.
The lake was discovered in 1905 by a thirteen-year-old boy named Ben Sands. As the story goes, Sands, who often played in the cave, happened upon a small opening and crawled through. The room was so large he was unable to see the ends of the room with his lantern, so he threw balls of mud in all directions and heard splashes. When he went back home and told people of his discovery, they were hesitant to believe him. By the time they went back down to explore it with lanterns, the water had receded, leading to the name "The Lost Sea."
The visible surface of the lake measures 800 feet long and 220 feet wide (4.5 acres) at normal "full" capacity. Cave divers have explored several rooms that are completely filled with water, without reaching the end of the cave. This exploration was conducted in the 1970s.
The caverns are filled with crystal clusters, stalagmites, stalactites, eerie rock formations and even an underground waterfall, the website for which is found here. The caves leading to Ruby Falls have a more dramatic collection of stalagmites and stalactites, in my opinion, but the falls are presented in a amusingly, dramatic way using coloured lights and music. Completely unnecessary considering the already surreal atmosphere of being underground in the pitch black darkness and hearing water falling from a long distance right beside you. It's like gilding the lily. I don't like the coloured lights at Niagara Falls either. What's with this strange tradition?
Just as a point of interest, the largest underground lake is found in Drachenhauchloch Cave in Grootfontein, Namibia. I'd include a picture but I can't find one.