I spent this past weekend with my son’s boy scout troop at the lava river cave just north of Flagstaff. It is an interesting geological feature that formed from an ancient volcanic eruption. (See the link for details on formation, well down the page.)
It was a pleasant stay in a commonly used campground a good quarter mile from the entrance. Unfortunately, there were a number of incidents of graffiti on logs and trees. Worse, about a month before we visited, vandals sprayed graffiti inside the cave, causing permanent damage.
Our troop did volunteer to help clean the graffiti off the cave walls, but that was done the weekend prior to our arrival. Because of how dark it is inside, we couldn’t really tell where it happened.