One look reassured me at once. A playful smile wreathed his lips, and lightened over his face a gleam of real benevolence, not unmixed, as I thought, with pity. Hesitating no longer, I preceded him into those realms of subterranean night. Down, down, down, I trod, until there seemed no bottom to the echoing cavern. Each moment the air grew heavier, and our candles began to flicker and grow dimmer, as the impurities of the confined atmosphere became more and more perceptible. My head felt lighter, and began to swim. My lungs respired with greater difficulty, and my knees knocked and jostled, as though faint from weakness. Still there seemed no end to the descent. Tramp, tramp, tramp, I heard the footsteps of my guide behind me, and I vainly explored the darkness before. At length we reached a broad even platform, covered over with the peculiar tiling found among these ruins. As soon as Pio reached the landing-place, he beckoned me to be seated on the stone steps, which I was but too glad to do. He at once followed my example, and seemed no less rejoiced than I that the descent had been safely accomplished. I once descended from the summit of Bunker Hill Monument, and counted the steps, from the top to the bottom. That number I made 465. The estimate of the depth of this cavern, made at the time, led me to believe that it was nearly equal to the height of that column. But there was no railing by which to cling, and no friend to interrupt my fall, in case of accident. _Pio was behind me!_ After I became somewhat rested from the fatigue, my curiosity returned with tenfold force, and I surveyed the apartment with real pleasure. It was perfectly circular, and was about fifteen feet in diameter, and ten feet high. The walls seemed to be smooth, except a close, damp coating of moss, that age and humidity had fastened upon them. I could perceive no exit, except the one by which we had reached it. But I was not permitted to remain long in doubt on this point; for Pio soon rose, walked to the side of the chamber exactly opposite the stairs, whistled shrilly, as before, and an aperture immediately manifested itself, large enough to admit the body of a man! Through this he crawled, and beckoned me to follow. No sooner had I crept through the wall, than the stone dropped from above, and closed the orifice completely. I now found myself standing erect in what appeared to be a subterranean aqueduct. It was precisely of the same size, with a flat, cemented floor, shelving sides, and circular, or rather _Aztec-arched_ roof. The passage was not straight, but wound about with frequent turnings as far as we pursued it.