Subway Cave is a 20,000 year old lava tube near Old Station, California.  It is a popular landmark near Lassen Volcanic National Park, its 0.25 mile cave resembling a subway tunnel.  For many this is their first time ever in a lava tube.  The cave is in great shape, resembling a typical Hawaiian lava tube w/ a noticeable aa floor w/ rocks firmly attached to the bottom.  Ceiling height here is as high as 20 feet w/ a three-way junction, the upper aa tongue path leading to a separate room.