"Yet it is very simple--when you know!" remarked Lotta, in high glee at my discomfiture.  "Follow me!"  And, dropping upon her hands and knees, she proceeded to crawl into one of the cavities that I had been searching, and which I should have declared was not nearly capacious enough to receive a full-grown man.  Nevertheless Lotta completely disappeared within it, and I after her.  When I had fairly entered the cavity I found that what had appeared to be its back wall, and which gave it the appearance of being only about two feet in depth, was really one of two side walls, a narrow passage turning sharp off to the right, just wide enough and high enough to travel through comfortably on one's hands and knees.  It wound round in what seemed to me to be about a half-circle of about fifty yards in diameter, and its inner end gave access to an enormous cavern, very roughly circular in shape, and about four hundred feet across in either direction.