The Best Sight in Washington Cascade Mountains and Valleys, Washington

Measuring nearly 2½ miles in mapped length, Ape Cave is the longest continuous lava tube in the continental United States. Two routes traverse the tube: the lower route is an easy hour-long hike, while the upper route is more challenging and takes about three hours. Bring at least two light sources (you can rent lanterns from the headquarters for $5) and warm clothing. In high season ranger-led walks are sometimes available; inquire at the Ape's Headquarters, off Forest Service Road 8303, 3 miles north of the junction of Forest Roads 83 and 90. Timed reservations are needed and can be booked at  www.reservation.gov for a $2 fee; a Northwest Forest Pass ($5 daily) is required for parking. The gate to Ape Cave is closed November through mid-May, though the cave can be reached by a half-mile trail from Trail of Two Forests Sno-Park off-season ($25 parking pass required).