Natural Bridges is a lava tube that collapsed leaving lava bridges. It’s located off of Forest Service Road 24 east of Trout Lake, Washington. Follow the signs to the location. The roads are pretty rough, so take your time. It’s a sort hike allowing you to loop around numerous lava bridges.
From Trout Lake, WA take Highway 141 for 4 miles past the Mt. Adams Ranger Station to the end of Highway 141. Continue west on Forest Road 24. Turn left on Forest Road 041 and go a half mile. Then turn right into the parking area.