[1] Along with nearby Cameron Cave, it became a registered National Natural Landmark in 1972, with a citation reading "Exceptionally good examples of the maze type of cavern development."

[3] A major difference is that Mark Twain Cave has a near total lack of speleothems, mineral deposits like stalagmites and stalactites in large open areas.

[7] The cave proved a popular diversion for mid-19th century Hannibal residents, especially children, including the young Sam Clemens.

Pioneering Hannibal physician Dr. Joseph Nash McDowell purchased the cave in the late 1840s and used it for several years as a laboratory for medical research on human corpses.

His belief that traditional burial 'stifled the soul of the dead', and a different type of interment would aid communication between living and dead, led to one of the cave's more notorious episodes, and inspiration for Twain, when McDowell placed his recently deceased child Amanda in a preserving coffin inside the cave work space.

[8][6] Twain's book Life on the Mississippi offered a description of the activities: In my time the person who owned it [the cave] turned it into a mausoleum for his daughter, age fourteen.

The body of this poor child was put in a copper cylinder filled with alcohol, and this suspended in one of the dismal avenues of the cave.However in 1849, when McDowell learned that locals had been daring each other to break into the cave and open the cylinder, disrespecting his child’s remains, he had the body removed for a more traditional, and safer, burial in the family vault behind the newly-built Missouri Medical College where he worked.

[9] Many in St. Louis believed that McDowell also used bodies stolen from local graves for his medical examinations, a not uncommon practice prior to the 20th century.

In September 1879, following the robbery of a train in nearby Saverton, Missouri, the cave proved a ready and secure hideout for few days rest.

It was said that one might wander days and nights together through its intricate tangle of rifts and chasms and never find the end of the cave.The cave was little known outside of the immediate Hannibal region until 1876, when Twain's landmark novel The Adventures of Tom Sawyer was published.

[6] The first regular tours by paying customers began in 1886 when local farmer John East charged tourists a dime to see some of the places inside the cave made famous by the novel.

[11] One cold winter day in 1925, Judge Evan Thomas Cameron's son Archie was caring for the family's cattle herd when he noticed steam rising from a sinkhole in the ground across the valley from Mark Twain Cave.

[13] The complex includes the Mark Twain and Cameron caves, a campground, a gift shop/visitors center, a candle shop, and a winery.