Ape Cave

The longest lava tube in the continental United States, formed by an eruption roughly two millennia ago beneath what is now Mount St. Helens country.

Field note

This is a true underground route with no installed lighting. Seasonal access uses timed reservations to protect the cave and control congestion.

Evidence line

This listing is marked documented. Practical details were last checked in July 2026. Conditions change, so use the primary source before leaving home.