8. Ape Cave – Washington
Contrary to what the name suggests you won’t find any apes in this cave, but you will have the chance to explore some of the longest lava tubes in the continental U.S.
These tunnels formed in thick lava beds when Mt. St. Helens erupted nearly 2,000 years ago.
Both the upper and lower tubes are open for exploration. At 3/4 miles long the upper is the shorter of the two, and offers a look at intriguing formations such as the “meatball”, a giant chunk of cooled lava that fell from the ceiling while lava flowed through the cave.
The lower tube is a longer and more challenging hike with boulder fields and lava falls to climb over. Aside from the cost of parking, visiting and hiking Ape Cave is free and open year-round.