When we had followed the thing into the archway and turned both our torches on the indifferent and unheeding group of three, we saw that they were all eyeless albinos of the same unknown and gigantic species. Their size reminded us of some of the archaic penguins depicted in the Old Ones' sculptures, and it did not take us long to conclude that they were descended from the same stock-undoubtedly surviving through a retreat to some warmer inner region whose perpetual blackness had destroyed their pigmentation and atrophied their eyes to mere useless slits. That their present habitat was the vast abyss we sought, was not for a moment to be doubted; and this evidence of the gulf's continued warmth and habitability filled us with the most curious and subtly perturbing fancies.

We wondered, too, what had caused these three birds to venture out of their usual domain. The state and silence of the great dead city made it clear that it had at no time been an habitual seasonal rookery, whilst the manifest indifference of the trio to our presence made it seem odd that any passing party of those others should have startled them. Was it possible that those others had taken some aggressive action or tried to increase their meat supply? We doubted whether that pungent odor which the dogs had hated could cause an equal antipathy in these penguins, since their ancestors had obviously lived on excellent terms with the Old Ones – an amicable relationship which must have survived in the abyss below as long as any of the Old Ones remained. Regretting – in a flare-up of the old spirit of pure science – that we could not photograph these anomalous creatures, we shortly left them to their squawking and pushed on toward the abyss whose openness was now so positively proved to us, and whose exact direction occasional penguin tracks made clear.

Not long afterward a steep descent in a long, low, doorless, and peculiarly sculptureless corridor led us to believe that we were approaching the tunnel mouth at last. We had passed two more penguins, and heard others immediately ahead. Then the corridor ended in a prodigious open space which made us gasp involuntarily – a perfect inverted hemisphere, obviously deep underground; fully a hundred feet in diameter and fifty feet high, with low archways opening around all parts of the circumference but one, and that one yawning cavernously with a black, arched aperture which broke the symmetry of the vault to a height of nearly fifteen feet. It was the entrance to the great abyss.

In this vast hemisphere, whose concave roof was impressively though decadently carved to a likeness of the primordial celestial dome, a few albino penguins waddled – aliens there, but indifferent and unseeing. The black tunnel yawned indefinitely off at a steep, descending grade, its aperture adorned with grotesquely chiseled jambs and lintel. From that cryptical mouth we fancied a current of slightly warmer air, and perhaps even a suspicion of vapor proceeded; and we wondered what living entities other than penguins the limitless void below, and the contiguous honeycombings of the land and the titan mountains, might conceal. We wondered, too, whether the trace of mountaintop smoke at first suspected by poor Lake, as well as the odd haze we had ourselves perceived around the rampart-crowned peak, might not be caused by the tortuous-channeled rising of some such vapor from the unfathomed regions of earth's core.

Entering the tunnel, we saw that its outline was – at least at the start – about fifteen feet each way – sides, floor, and arched roof composed of the usual megalithic masonry. The sides were sparsely decorated with cartouches of conventional designs in a late, decadent style; and all the construction and carving were marvelously well-preserved. The floor was quite clear, except for a slight detritus bearing outgoing penguin tracks and the inward tracks of these others. The farther one advanced, the warmer it became; so that we were soon unbuttoning our heavy garments. We wondered whether there were any actually igneous manifestations below, and whether the waters of that sunless sea were hot. Alter a short distance the masonry gave place to solid rock, though the tunnel kept the same proportions and presented the same aspect of carved regularity. Occasionally its varying grade became so steep that grooves were cut in the floor. Several times we noted the mouths of small lateral galleries not recorded in our diagrams; none of them such as to complicate the problem of our return, and all of them welcome as possible refuges in case we met unwelcome entities on their way back from the abyss. The nameless scent of such things was very distinct. Doubtless it was suicidally foolish to venture into that tunnel under the known conditions, but the lure of the unplumbed is stronger in certain persons than most suspect – indeed, it was just such a lure which had brought us to this unearthly polar waste in the first place. We saw several penguins as we passed along, and speculated on the distance we would have to traverse. The carvings had led us to expect a steep downhill walk of about a mile to the abyss, but our previous wanderings had shown us that matters of scale were not wholly to be depended on.

Alter about a quarter of a mile that nameless scent became greatly accentuated, and we kept very careful track of the various lateral openings we passed. There was no visible vapor as at the mouth, but this was doubtless due to the lack of contrasting cooler air. The temperature was rapidly ascending, and we were not surprised to come upon a careless heap of material shudderingly familiar to us. It was composed of furs and tent cloth taken from Lake's camp, and we did not pause to study the bizarre forms into which the fabrics had been slashed. Slightly beyond this point we noticed a decided increase in the size and number of the side galleries, and concluded that the densely honeycombed region beneath the higher foothills must now have been reached. The nameless scent was now curiously mixed with another and scarcely less offensive odor – of what nature we could not guess, though we thought of decaying organisms and perhaps unknown subterranean fungi. Then came a startling expansion of the tunnel for which the carvings had not prepared us – a broadening and rising into a lofty, natural-looking elliptical cavern with a level floor, some seventy-five feet long and fifty broad, and with many immense side passages leading away into cryptical darkness.

Though this cavern was natural in appearance, an inspection with both torches suggested that it had been formed by the artificial destruction of several walls between adjacent honeycombings. The walls were rough, and the high, vaulted roof was thick with stalactites; but the solid rock floor had been smoothed off, and was free from all debris, detritus, or even dust to a positively abnormal extent. Except for the avenue through which we had come, this was true of the floors of all the great galleries opening off from it; and the singularity of the condition was such as to set us vainly puzzling. The curious new fetor which had supplemented the nameless scent was excessively pungent here; so much so that it destroyed all trace of the other. Something about this whole place, with its polished and almost glistening floor, struck us as more vaguely baffling and horrible than any of the monstrous things we had previously encountered.

The regularity of the passage immediately ahead, as well as the larger proportion of penguin-droppings there, prevented all confusion as to the right course amidst this plethora of equally great cave mouths. Nevertheless we resolved to resume our paper trailblazing if any further complexity should develop; for dust tracks, of course, could no longer be expected. Upon resuming our direct progress we cast a beam of torchlight over the tunnel walls – and stopped short in amazement at the supremely radical change which had come over the carvings in this part of the passage. We realized, of course, the great decadence of the Old Ones' sculpture at the time of the tunneling, and had indeed noticed the inferior workmanship of the arabesques in the stretches behind us. But now, in this deeper section beyond the cavern, there was a sudden difference wholly transcending explanation – a difference in basic nature as well as in mere quality, and involving so profound and calamitous a degradation of skill that nothing in the hitherto observed rate of decline could have led one to expect it.