There are fifteen salt mines in the United States and Strataca is the only one you can go down. It sits in the working Hutchinson Salt Company mine in Hutchinson, Kansas, and it takes visitors 650 feet below the surface into one of the largest rock salt deposits in the world, laid down 275 million years ago. It was previously called the Kansas Underground Salt Museum.
The mine has been running since 1923, when it opened as the Carey Salt Company, and it works by room and pillar: a shaft is sunk through the overlying rock to the salt, then the salt is taken out in a checkerboard, with large square caverns alternating with square pillars of salt left in place to hold up everything above. The pillars here are 40 feet square. That pattern is not only structural; it is also what keeps ventilated air circulating where people are working.
The scale takes some grasping. The mine covers about 980 acres, and if you laid all the excavated rooms end to end the corridor would run 150 miles.
A salt mine is dry and chemically stable, and that has made these workings valuable for something other than salt. Underground Vaults & Storage operates in the mine, holding film masters including Gone with the Wind and Ben Hur, television masters, medical records, oil and gas charts and documents from all fifty states and many other countries. The museum shares a shaft with them; the two organisations split the cost of sinking it, which is the only reason the museum could open at all.
Some of what is stored down there goes on show. A rotating exhibit has displayed the Batman and Mr Freeze costumes from Batman & Robin, James Dean's shirt from Giant, and the Snowman from the 1998 film Jack Frost.
Visitors ride electric trams driven by docents for the Dark Ride section, and the Mantrip Gallery holds two of the train-like vehicles that carried miners to the face.
Other places on the map within a couple of hours.
