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.  There is however a section of the cave that is not often visited by the general public to which the cave extends another 1,000 feet.  The cave is in great shape, resembling a typical Hawaiian lava tube w/ a noticeable aa floor w/ rocks firmly attached to the bottom.  Only the vandals seem to leave there mark down this part of the cave, where graffiti abounds especially downwards towards the end.