Nothing immediately happened. There were no hordes of spectators instantly swarming into its newly-revealed entrances. Goblin Cave had no clue where its new entrances let out; it had no clue where its original entrance let out. It could not see outside of its dungeon.
Goblin Cave had known that its senses didn't directly correlate with the senses of adventurers or its spawns for a long time. Since it was first delved, in fact. It could determine structure, shape, and color irrespective of light. And so, it knew that there was light cast on its entrances, and that light waxed and waned over time, but it had only the barest concept of why that would be. Its books spoke of days and nights, a sun and the moons, each with a certain tone of light, and each moving in the sky — changing the angle of light that fell on its entrance. It could see that much. But looking outward... it seemed impossible. Whatever its senses did, they were one with its mana cloud. It was always looking inward at itself.
This had long been a frustration for it, and now it had spare entrances to experiment with. Goblin Cave focused on this, in favor of dwelling on its nervousness. It could feel light; it knew how to operate on light. What it wanted was... something that could capture the light falling into it and then display it in a fashion it could understand? Something that captured the light and then redisplayed it? But surely that was just what the light already did; if it replicated that, then it would simply be seeing more light spilling across its floors. Adventurers, mobs, they tended to have specialized sensory organs. Eyes. They did something, even before they entered the mess of the nervous system that it had never been able to fully comprehend. They focused light in the way it focused mana, angling the light to meet at a focal point.
Goblin Cave summoned up a box of voidstone, ink black on the inside. In the center of one wall, it attached a shard of brilliantly-glowing manacrystal. The inside of the box was flooded with light, but that would, it knew, appear no different to a creature inside it: the voidstone walls absorbed all the light, so that the box's interior was still "just as dark", save for the manacrystal itself. It added, opposite the manacrystal, an opaque slab of smooth quartz. That appeared lit, now. But what it wanted... was some kind of lens that would bend the light to all focus on a single point.
In between the two, hanging in the middle of the box, it made a glass lens. It shaped the lens, changing structures within it and redirecting the stream of light, and as it did so it watched the warping and shifting image across the quartz slab. Light slowly formed a projected image: the light, diverging from the manacrystal, was brought back into alignment by the shaped lens, forming a distinct image on the quartz backdrop. Goblin Cave moved the lens back and forth, watching as that made the resulting image more or less blurry, and how when it boxed out an interior divider, blotting out the unfocused light, the image got much more distinct. Yes, that was it: it couldn't capture all the light, since that would result in the same vague illumination it already received. By capturing only a small point of light, and focusing it, it could project an image.
Goblin Cave constructed a tube for its lens, with an interior quartz wall, and extruded a few throughout its interior hallways to test. There was a relationship between the size of the lens, the focal length of the lens, and the distance from any lit element. Also, perceiving an environment from a flat projection was a disorienting experience. Everything was blurry and all the angles were wrong. When it looked at a cube, it saw a cube. When it looked at the flat projection of a cube, the sharp right angles were projected as warping, wobbling divisions that changed as it rotated the cube. If it hadn't already known the environments it was projecting onto quartz, it wouldn't have been able to identify them from projection alone.
But, like everything else, it was a process it would have to learn how to use and iterate on as it made further developments. In the mean time, it assembled a mana lock on one of its entrances and ringed the lock with twenty eight projection tubes, each angled slightly differently, and watched their backplates intently.
For its first glimpse of the world exterior to itself, the result was underwhelming. A smear of intense cyan across half the plate, with a jagged latticework of green and red-orange partially intersecting it. A few of the tubes on the left side of the mana lock were angled so that something else was visible: the source of the light, a brilliant circle that emit with such force that the concentrated light started to etch lines in its backing quartz. There were swells of grey; that at least it could interpret: granite boulders, some of which had landed partially within the boundary of its entrance. Everything was moving slightly, warped in a way that at first it took for an aberration in its lenses, but on further testing seemed to be accurate to whatever was out there. Motion like the rippling of water. Greens and browns and cyans shifting. It extended the length of its tubes, warping the lens to match, and watched as that made some shapes more diffuse and others more stark. So. This was the world outside of itself: a riot of colors and shapes it had no capacity to comprehend.
It would have to keep testing. It would also have to record the lights. More than anything else, what came to it from the outside world was ephemeral: it had no capacity to recall and recreate anything there. If the light changed — as it was lead to believe it would — it would have no knowledge of why or how to reconstruct what had been. It would only have its vague memories of an incomprehensible blur.
That part, at least, was solvable. It spun up a new control node for the mana lock, and assigned it etching duty. Every few intervals, it would inspect the light incoming on its backing plates and create a slab of manastone, marbled such that its output matched the hue and intensity of the incoming light. Then, after the first interval returned seven plates that drew tenfold the mana it expected in an attempt to render the brilliant circle with high-intensity manastone, it amended the command: match the intensity up to a certain limit.
It replicated the same configuration for another eye, this time with a variation: all the tubes pointed in the same direction, but with different lengths. This produced many variations of the same image, with blurs at different intervals. The repetition at least let it pick out some similarities: grey-and-brown blurs in one half of the image, mostly cyan in the other, with a rippling band of orange-and-white tones between.
It constructed the same configuration of tubes within floor 51, aiming it at its rippling lake and the budding fungal beds that lined its shore. The varied tube length conveyed distance: it could tell, now, that the cluster of mushrooms that were closer to the tubes formed differently-sized blurry splotches on different tubes, compared to more distant mushrooms on the far bank. The tube length provided an analogue of depth, which meant that it could attempt to reconstruct a spatial comprehension from a series of flat panels.
On its third entrance, it combined the two prior concepts: twenty eight different-length tubes, placed in twenty-eight sets ringing the mana lock, all angled different directions.
This was a truly gargantuan amount of information. Goblin Cave peered at the images, slotting them in distance-order to make a vague approximation of their depth. Granite boulders, closer, followed by a strange warping shape that it thought might be a slope of loose gravel. Surfaces that changed in distance and altitude were even more difficult for it to reason about just from the light. This particular entrance had surfaced in a rocky lull between mountain crags, it thought: there was considerably more granite-grey visible, with only a rough triangle of cyan.
These, it recorded in cubic blocks, making each wafer-thin slice of manastone separated from the others by a thin gap of open space, in an attempt to spatially-structure the images.
Time passed, but only a little. The cyan in the images diminished to blue and then a deep indigo, in time with the brilliant circle shifting location. The sun, perhaps. The books spoke of the sun lighting the sky, and so as the sun waned, so did the light overall. Eventually a new glowing shape emerged, visible from two of its entrances: a pale purple crescent, at less than a sixteen-thousandth the intensity of the sun. A moon, perhaps. Goblin Cave had to instruct its recording nodes to add a minimum threshold for lighting, as well, to prevent these images from being utterly overwhelmed solely from the faint light of its manastone walls.
A night and a day passed, giving it nearly seven hundred plates per tube. One adventuring party left its old entrance, and two more entered, separated by a gap of roughly ten hours. No sign of them detecting its new entrances. There had been moving blurs across its images, which it still couldn't decypher: some kind of animal, perhaps? But not one it had unlocked, and so not one in had any kind of spatial intuition for how it was shaped. The thought of life outside of its system categories was tantalizing, but the process of analyzing flat images to reconstruct shape — it had the feeling that, much like spawning a [Flame Wisp], this would be something it would approach in dozens of angles just to make almost-zero progress.
If it was to keep its imaging running, it would need a more serious solution for storage. The length of the day gave it an idea, though: it carved out a spiraling ramp with an open center, and aligned it so that each spiral was divided into precisely six hundred eighty six segments, one for each imaging it took per day. Then, the spiral descended into the ground, with each revolution marking one day, forming a winding path. This way, it could easily compare any given day's recording with the prior day's, because they were spatially aligned directly above each other.
That being said... Goblin Cave would have to pay attention to the day length. The books it had read had mentioned seasons, times of light and of darkness. It had no clue what the variation was, or how long a day truly was. It had just lined the images it had up so that the incidences of minimal and maximal brightness mostly coincided.
It restructured its entrances, giving them a uniform layout: mana lock with 28-upon-28 mana tubes just past where the furthest boulders had fallen, offshoot chamber to hold recorded images springing off from that, and then a smooth, unbroken corridor sloping down to eventually meet its mana bellows.
Analyzing the images was a productive way to direct its nervous energy. Every moment that passed without anything new happening just increased the tension. Something was bound to happen, but it had no idea of when. How long had it taken for its dungeon to be discovered, what was coming up on sixty-five years ago? It had been some time. But its initial entrance had been a shallow rock shelf in a lull, mistakable for an inch-deep cave. Its new entrances — they glowed. It hadn't fully considered that until it saw the darkness of night. Even the faint manastone glow, shrouded by murky glass, still lit up the nearby boulders, reflecting a deep blue back into its own imaging tubes. Perfectly square eruptions of dungeon-stuff into the surrounding mountainsides.
Another day passed. Goblin Cave began to make out some vague structure in its images as it strained to comprehend its glut of images. Linear shapes, curving shapes. It comprehended the gravel slope as thousands of rough-edged stones, rather than an incoherent blur it could only vaguely assign a direction to. The moving structures were something like its fungi stalks: vegetation, probably. They grew with heavy gills in overlapping shrouds, and all their flesh was either rich green or a toxic-looking red-orange. It inspected its images, struggling to comprehend each aspect of them.
Then, somebody stumbled across one of its new entrances.