Update: Unfortunately this cave has collapsed and is no longer accessible.
You can reach Cave Falls by road east of Ashton, Idaho. It is just inside the southwestern boundary of Yellowstone National Park. This is the park's widest waterfall at over 250 feet. While it’s only twenty feet high, the entire Falls River drops twenty feet here in a spectacular display.
Cave Falls' name comes from a large cave that can be found just off to the side of the falls. Hikers can walk into the cave, which is over 20 feet tall and 100 feet wide. There are several other short trails that lead to an assortment of views of the falls.