El Calderon is a low cinder cone on the western edge of the monument, with the most accessible cave hike in the park: a roughly three-mile loop that takes in the cone, a small bat cave and Junction Cave, a long lava tube that you can scramble through with a torch. The cave floor is rough but largely flat, and the experience is genuinely cinematic — sunlight from collapsed skylights, a constant cool draught, and absolute silence once you are inside.
The bat cave is closed from April to October to protect the resident bat colonies; outside that window you can peer in but not enter. Stop at the visitor center in Grants first to pick up a free permit and the latest news on closures. Pack a head torch — torches are required even on the daytime loop.