The Lost Sea isn’t really lost so much as it’s not visible above ground. And it’s not really a sea so much as a lake.

It’s still worth the trip. Located in Sweetwater, Tenn., this underground lake offers boat tours. It holds the title of America’s largest underground lake, certified by Guinness World Records.

Before you can see the “sea,” there’s a ¾ mile walk with an incline through the Craighead Caverns, so be prepared. (Note: The caverns also offers a “wild tour” where more adventurous spelunkers can crawl around some lesser known areas.)

The caverns have been well known for centuries. They were used as council chambers for a group of Cherokee natives, for gathering saltpeter to make gunpowder during the Civil War (graffiti with the date 1863 has been carbon-dated to that time), a tavern and moonshine stills in the 1940s, and a fallout shelter in the 1950s.

But the lake itself, which covers 4.5 acres, was undiscovered for many years. It was first discovered in 1905 by 13-year-old Ben Sands, who found an opening during a drought when water levels were low. According to our guide, no one believed the boy at the time and it would be another six decades before a group of explorers found the opening again and began to study the unusual underground lake.

When your tour group arrives at the lake, you’ll see a dock with several boats. Loading up is interesting, as some folks tend to rock the boat. The lake ride itself is short but fascinating.

The lake’s rainbow trout were introduced by researchers who hoped to tag them and follow them out of the cave to see where it flows. The fish are handfed and “spoiled,” however, and refused to leave the clear water with a constant temperature of 56-degrees. Lights in the water keep the fish from becoming “cave-blind” and they live happy lives and grow fat, the guide said.

The Lost Sea opened to the public in 1965. These days, the water level is carefully maintained and any extra water is used to run the gift shop and small village of shops aboveground. The shops, a general store, ice cream parlor and glass blower, are closed from October to mid-March but the cave is open year-round. Admission is $25 for adults and $15 for kids and reservations are best made online because spots sell out quickly.

If you plan to stay a few days, check out the nearby RV parks and campgrounds. Need an RV? Visit RVshare.com.