Returning in the same direction, we entered a thick grove, in which we dismounted and tied our horses. It was the finest grove we had seen in the country, and within it was a great circular cavity or opening in the earth, twenty or thirty feet deep, with trees and bushes growing out of the bottom and sides, and rising above the level of the plain. It was a wild-looking place, and had a fanciful, mysterious, and almost fearful appearance; for while in the grove all was close and sultry, and without a breath of air, and every leaf was still, within this cavity the branches and leaves were violently agitated, as if shaken by an invisible hand. This cavity was the entrance to the poso, or well, and its appearance was wild enough to bear out the wildest accounts we had heard of it. We descended to the bottom. At one corner was a rude natural opening in a great mass of limestone rock, low and narrow, through which rushed constantly a powerful current of wind, agitating the branches and leaves in the area without. This was the mouth of the well, and on our first attempting to enter it the rush of wind was so strong that it made us fall back gasping for breath, confirming the accounts we had heard in Nohcacab. Our Indians had for torches long strips of the castor-oil plant, which the wind only ignited more thoroughly, and with these they led the way. It was one of the marvels told us of this place, that it was impossible to enter after twelve o'clock. This hour was already past; we had not made the preparations which were said to be necessary, and, without knowing how far we should be able to continue, we followed our guides, other Indians coming after us with coils of rope. The entrance was about three feet high and four or five wide. It was so low that we were obliged to crawl on our hands and feet, and descended at an angle of about fifteen degrees in a northerly direction. The wind, collecting in the recesses of the cave, rushed through this passage with such force that we could scarcely breathe; and as we all had in us the seeds of fever and ague, we very much doubted the propriety of going on, but curiosity was stronger than discretion, and we proceeded. In the floor of the passage was a single track, worn two or three inches deep by long-continued treading of feet, and the roof was incrusted with a coat of smoke from the flaring torches. The labour of crawling through this passage with the body bent, and against the rush of cold air, made a rather severe beginning, and, probably, if we had undertaken the enterprise alone we should have turned back.