America’s Largest Underground Lake Is Hidden 140 Feet Below the Surface—How to Visit

Tennessee is one of those states where natural wonders appear both above the ground—in places like the Tennessee River Gorge and Great Smoky Mountains National Park—and hundreds of feet below the surface. There are several cave systems that snake across this part of the country, creating a vast underground landscape of chambers, tunnels, rivers, waterfalls, and lakes. One of the more impressive subterranean sites open to visitors is known as the Lost Sea, an aquatic landmark that claims the title of the largest underground lake in the United States.

Part of the Craighead Caverns cave system, the Lost Sea is located near Sweetwater, a small city in the foothills of the Smokies, right between Knoxville and Chattanooga. While the lake is said to have been discovered in 1905 by a 13-year-old boy named Ben Sands, the surrounding caverns were used by the Cherokee, and 20,000-year-old jaguar tracks were also found there. Today, only about 13 acres of the body of water have been mapped; as of 2026, no end of the lake has been found. The portion of the lake visible to the public is about 4.5 acres, but there is a series of rooms, all filled with water, below. 

“It is simply amazing to see such a large body of water so far underground. It always makes me think of what else that might be underground that we don’t even know about,” Lisa McClung, general manager at the Lost Sea, tells Travel + Leisure. “It is majestic and mysterious and simply beautiful. Definitely something you do not see every day.”

Here’s how to plan a trip. 

Things to Do

The main attraction at the Lost Sea is, unsurprisingly, the lake itself, and you’ll join one of the guided tours, offered on the hour throughout the day, to see it for yourself. From start to finish, the experience lasts about an hour and 15 minutes. The journey includes a 0.75-mile round-trip walk along wide, steep pathways, and an education on the history and geology of the cave, lake, and rare formations, like the delicate crystalline structures known as “anthodites” or “cave flowers.” Once you reach the bottom of the cave, you’ll board a boat and ride across the Lost Sea. 

“For me, the most exciting part of the tour is to hear the gasps when people reach the lake room. They are looking at such a large body of water, it is almost unbelievable,” says McClung, who adds that visitors are also surprised by the size of the cave. “Most people expect tight spots that are hard to get through, and most of the rooms in our cave are huge and could easily fit a two-story building inside.”

Either before or after the tour, visitors are encouraged to explore the Lost Sea Village, open seasonally. Here, you’ll find a wooded village with a general store, glass blowing gallery, candy shop and ice cream bar, picnic facilities, a nature trail, and a gem mine attraction. 

How to Visit

There is no “best time” to visit the Lost Sea, as it’s open year-round—with the exception of Thanksgiving and Christmas Day—and the cave itself remains at a constant 58 degrees Fahrenheit. That said, McClung notes that the temperature “feels great in summer and winter,” and summers tend to be busier. “I would love to encourage people to purchase tickets ahead of time, especially in the summer months when we see the majority of our visitors,” she says. A standard adult ticket costs $28.95, and a standard child (ages 4 to 12) ticket will run you $16.95; there are discounts for seniors, military adults, and military children, and children 3 and under receive free entry.  

Once you’ve secured your tickets, you can start planning other aspects of your East Tennessee adventure—namely, your accommodations and other activities to add to your itinerary.  “There are many new Airbnbs located in Sweetwater. Most of these are within walking distance of downtown Sweetwater, which has several restaurants, ice cream shops, coffee shops, and antique shops,” says McClung. “That is usually my first recommendation. I think visitors can really experience the true small-town feeling that way.”

While you’re in the area, she also suggests visiting a few other highlights, including Tsali Notch Vineyard, Sequoyah Birthplace Museum, and Fort Loudoun State Historic Area. “All of those are fairly close to the Lost Sea,” she adds.