Like nearby Black Butte and the Metolius River, Skylight Cave is another fascinating result of volcanic activity in Central Oregon. The cave is actually a lava tube that was formed when lava flow temperatures closer to the surface cooled more quickly than the lava beneath it; as the lava flow continued and eventually stopped, the hard layer remained in tact over an empty space.
Skylight Cave is so named for sections in the cave's upper layer that have fallen through, allowing for dramatic shafts of light to filter through at certain times of day (usually in the morning). The entrance to the cave is a hole in the ground where the roof of the lava tube has caved in. You'll find a ladder that descends into the opening; descend and head left to the main large cavern with the three skylight openings, or head right to see how far into the lava tube you can go.
If you decide to head right, the ceiling height quickly diminishes as you go further into the lava tube. There are points where crawling on your belly in the cold, damp dirt is the only way to advance to the next section. Bringing a helmet or some kind of head protection isn't a bad idea, as it is easy to forget about the low ceiling height, and the cave ceiling is jagged and unforgiving.
Cave temperatures remain a cool 40 degrees in the summer, so bring layers. Also keep in mind that the cave is damp and the surfaces are abrasive. Two light sources, a primary and a backup, are highly recommended for any cave exploration. Sunset Cave is closed from September 30 through May 1 to protect hibernating bats.