Onyx Cave, about 6 miles east of Eureka Springs, Arkansas, has welcomed visitors since 1893, making it the state's oldest show cave. Although its name suggests true onyx, its formations are actually flowstone, once widely marketed as “cave onyx,” a naming trend common in the late 19th and early 20th centuries. The cave continues to operate as a tourist attraction with guided audio-headset tours. Because it has only one public opening, visitors exit the same way they enter. Its interior stays near 57 °F year-round. In 1969, scenes for the B-movie It’s Alive were filmed there, and in October 2017 the cave and surrounding acreage were offered for sale for $500,000.

Holiday Island, Arkansas · USA