As a boy, crags and cliffs had always had a strange fascination for him; and for hours together, while still too weak to walk more than a few yards at a time, he would watch the birds circling around the spur at the north-eastern extremity of the village. He noticed that hundreds of these birds disappeared into a narrow cleft, which seemed from the base of the cliff to be no more than a couple of feet in height. For some days he was content to note the fact, but as his strength returned, he felt the impulse of a born cragsman to explore the cleft. It was clearly a hazardous undertaking, for the spot in question was some two hundred feet above the ground, and the face of the cliff was almost perpendicular. Above the cleft the precipice jutted out at a considerable angle, rendering any attempt to reach it from above impossible. There were, however, traces of a narrow ledge along the face of the cliff, running from the desired spot for some distance parallel with the ground, and then sweeping gently downwards to a point some fifty feet above the surface, where it suddenly ceased. Tom resolved to attempt the ascent, and not all the entreaties of Mbutu could turn him from his purpose. Armed with an improvised alpenstock, and a grappling-hook to aid him in clinging to the face of the cliff, he reached the ledge with some difficulty, owing to the loose nature of the soil. But once on the ledge his progress was more rapid, and in less than half an hour from the start he found himself at the entrance of an extensive cavern in the side of the cliff. The opening was, for the most part, hidden from view by a large mass of loose rock that had fallen from the roof. The slope of the cavern led upward, and although he soon found himself in darkness, Tom was surprised to find that the air was quite pure. At the expense of his shins, he groped his way upwards, disturbing on the way innumerable bats and birds, which cannoned against him in a panic rush for the open air. After some thirty yards of toilsome progress he came to a sudden stop, discovering as he did so the reason why the cavern had none of the vault-like stuffiness which he associated with many similar adventures at home. Through a cleft in the rock ahead filtered a thin beam of light, but there was no passage even for Tom's lithe frame, wasted though it was by a month's illness. Tom was curious to know at what point of the cliff he had arrived, and, returning to the opening of the cavern, he made signs to Mbutu to betake himself to the hill overhead.