Mammoth Cave is a lava tube near Tionesta, California.  I've been here about five times & have never fully explored it, though I've heard it has about 1.59 miles of passages.  The cave itself has high ceilings initially but then it becomes a continuous crawling maze of intricate passageways through wet mud & ropy pahoehoe.  This is the first main junction room yielding a beautifully colored passageway w/ old pahoehoe flows covered in sand on the floor, intricate cracks and golden hydrophobic bacteria on the ceiling.  All the small holes in the sand are from water droplets falling off the small lavacicles on the ceiling - each droplet carries small amounts of sand particles which as you can see has filled up a lot of the passageways.  A visit in January 2015 I got extremely disoriented deep inside & lost for about 45 minutes as I kept repeating my tracks before remembering that the entrance is higher up & the cave itself gradually slopes downwards in elevation.  From there I was able to find my way out.  This next time that I visited seven months later, there was a dead dog exactly where I had gotten lost last time, there was nothing but dog tracks everywhere & it eventually died of starvation in there.