Thought to be the longest lava tube in the Western Hemisphere, the 12,810-foot tunnel was found within a massive lava flow that oozed from the volcano almost 2,000 years ago. Flowing downhill, the stream of lava cooled and formed a hard crust atop the hot lava. In time the lava drained and left an intricate, winding lava cave behind.
The cave was first explored in 1946 by the St. Helens Apes - the local Boy Scout troop for whom the cave is named.
Visitors should have three light sources, sturdy shoes and a jacket; the temperature is about 42 degrees Farenheit.
