The coast redwood shown is Caveman, found one year when Thomas from Germany explored with me, looking for New Hope, up Clark's Creek in Jedediah Smith Redwoods State Park.
Goosepens in redwoods are not hard to come by, but entire rooms inside are definitely uncommon. The Church redwood is one other that comes to mine, also in the same park. The base of Caveman is relatively large. The downslope side has a doorway to enter, and there is a "window" on another side. It could easily be used for temporary lodging. Its protected from wind and rain, and has enough space for several people to comfortably sleep inside. This redwood is on a slope, and in the second photo, the top of my head would be like a foot or two beneath my feet in the top image.