Nickajack Cave in Marion County may not be open for cave exploring as it once was, but it is still quite popular for bats – and for viewing bats.

“It is a wonderful resource,” said Mike Bailey, a wildlife officer with the Tennessee Wildlife Resources Agency. “Anything that deals with bats is a wonderful resource. Bats are some of the most important animals on the face of the earth.”

In recent years, a viewing platform at the end of a trail has been set up, and visitors can view the bats coming and going, including in the spring, when female gray bats give birth and raise their young.

Mr. Bailey said the gray bats come to Nickajack because it has the ideal cave features needed: a domed ceiling, 100 percent relative humidity inside, and a large amount of surface water from a flowing stream inside.

“Less than five percent of caves have this,” he said.

While bats still come and go in the cave, humans do not. Up until a few years ago, humans not only regularly visited he cave, however, they also extracted resources.

For a period in the 1800s, saltpeter was mined. Through the early part of the Civil War, Confederates extracted the saltpeter for use in the manufacture of gunpowder. After the Union captured the cave, the mining ceased.

“The Union said the capture of Nickajack Cave was more important than the capture of Chattanooga,” said Mr. Bailey.

Over the years, the cave was owned privately, and cave explorations took place.

Noted nature writer Edwin Way Teale walked through the large cave with his wife and included his experiences in his popular 1951 book, North with the Spring.

He wrote of being in the cave at different times of the year and hearing the shrill of multiple species of bats, of seeing blind crayfish, and of traveling more than a mile through the water and coming upon Mirror Lake below where Tennessee, Alabama and Georgia meet.

He also wrote that he heard that the largest stalagmite in the world was in the cave.

Wandering through Winter, a later book Mr. Teale wrote in this same seasonal travel series, won the Pulitzer Prize in 1966.

Another person who knew how to pen words – singer Johnny Cash – visited the cave at a time when he was undergoing an inner civil war. High on drugs and alcohol, he planned to take his life. But he fell asleep in the cave, and when he awoke, had a change of heart. He was able to see a light that led him out of the cave and soon saw an inspirational light and turned his life away from drugs.

In the 1960s, after nearby Hales Bar Dam was considered irreparable, Nickajack Dam was constructed. As a result, the lower part of the cave entrance was flooded by TVA when Nickajack Reservoir was built, and a gate was later put across the entrance.

“Anytime you flood a cave it is kind of a sad thing,” said Mr. Bailey. “Caves are some of the most delicate biological habitats on the face of the earth.”

While humans may be disappointed, the bats seem to be only mildly affected. They still head out at dusk to eat some bothersome insects, giving humans watching them one more reason to appreciate them.