For 2017 Glenwood Caverns will be opening the world's first underground drop tower. The drop tower itself will be built by Soaring Eagle and they are working with a St. Louis based company called Creative Visions for the theming and hologram inside the mineshaft. Here are some pictures of the mineshaft the ride will be using:
And here's what the ride building looks like currently:
The park is working hard to get this open by the end of July as they originally planned for July 4th, but obviously missed that. The ride also only has seatbelts similar to this other drop tower by Soaring Eagle: