When she found it, Twilight had known it was special. Perhaps just another wonder the Everfree had spit up, but it was special none the less. Nopony had noticed it for years, partially because few dared to enter the Everfree, and also due to the fact the entire structure was covered in overgrowth.
Half of it was buried underground, and the half that was aboveground was so choked with vegetation that excavation it was proving difficult. It was built up of stone blocks larger than most ponies, and though none knew how old it was, the craftsmanship was still apparent.
Princess Twilight oversaw the archeological program attempting to uncover what exactly she had found. So far the best guess was a tomb.
The whole structure was roughly two stories tall, though it was unknown how far below the earth it went. Spells designed to measure the depth of caves had failed to properly function for unknown reasons.
This just caused Twilight to want to see what was down there even more. Princess or not, she was still a scholar at heart. Unveiling the unknown was her duty. It had absolutely nothing to do with exploring an ancient ruin Daring Do style. Nope. Not one bit.
Shame that Rainbow Dash was away in Cloudsdale for the week. She would love to explore the place. Even though there was a decent chance she might accidently break some four thousand year old relic or something.
Standing in front of the whole place, she saw what must have been a rather large entrance. A solid stone door blocked it. Above the door was a weathered and broken inscription in a language the princess was not familiar with.
Carcere Mortis
With the assistance of a few unicorns that were part of the excavation team, the great stone that prevented entrance was removed. Twilight led a small group into the depths of the tomb. They were surprised to find yet another great stone door, but to their alarm, there were skeletons propped up against the door. Upon inspection, they were in fact pony skeletons.
"A past archeological team perhaps?" Sandy Bones, an earthpony part of the group offered. She ran a hoof through her hair.
"Doubtful, look at how old the bones are, and their position. We may be looking at the builders of this place." Damp Lantern, a unicorn, replied. He rubbed his chin in thought.
"Well, let's get this door moved as well, and somepony get another group to carefully remove the bones. See if we can find out who there were, and why they were here." Twilight asked.
"Of course your Highness!" One in the group chimed in, and took off.
"Damp, care to help me with this door? Doesn't seem as large as the last one." Twilight offered.
Upon removal of the second door they were shocked at what lay in the room ahead of them. Another door, slightly smaller then the last, and more bones. The bizarre thing being that these bones belonged to Griffins.
"A multi-species project to construct this perhaps? But for what purpose?" Damp Lantern wondered. "Assuming this structure is in fact older than Equestria's founding, what could have motivated them to build something of this scale?"
Another door removed. More bones. Minotaur this time. Remove bones for study, open door. A cycle was beginning to form.
Another door removed. More bones, sort of. Changeling exoskeleton remains.
"What on earth is this place?" Sandy Bones whispered.
They removed the remains, and opened the next door as they had for the rest. What they found was a damp room, the walls, the floor and ceiling were made of stone. On the far side of the room was a half-spherical that lead down, into a black abyss. Littering the floor were bone fragments, apparently millennia old.
"Sandy, Damp, come with me further into the complex. The rest of you stay, and find anything you can." Princess Twilight commanded.
The trio went through the doorway, and down the incline into the black.
"Light Spell." Twilight instructed. Damp Lantern obliged. Two magical sources, one purple, one blue, illuminated stone that had not seen light in an eternity. Even still their artificial light penetrated the darkness by only a few meters.
Sandy Bones shuddered for a moment, clearly uncomfortable. This place gave her heebie-jeebies. She shook her head and flicked on a flashlight. There was exploration to be had. No bad feeling would deter her from it. The group proceeded forwards at a slow pace.
"You know, usually locations like this are covered ceiling to floor with booby-traps." Damp Lantern joked.
"Ah ha ha ha." Sandy muttered sarcastically.
"Even still, watch your step. No clue what's down here." Twilight pondered. As if in response, there was a quiet clicking noise a distance away, followed a pitter patter that was most likely the footsteps of a rat. Twilight shuddered, and Sandy grimaced. Damp Lantern chuckled, and as he did, brushed up against something on the wall.
"Would you look at that. A torch holder." He said, clearly amused. With a very small fire spell, the torch it held was lit. What they were not expecting was for torches further down the tunnel to light in response, as if linked.
"Magic?" Sandy wondered.
"More than likely, but why something so complicated? Why not a triggered light spell, or illuminating crystals?" Twilight asked. Neither of her companions could give a valid answer. They pressed onward down the now much brighter tunnel. They were joyous to find inscriptions chiseled into the stone walls.
"I can't make out the language, but look!" Sandy pointed out. Depictions of figures bowing to a skull atop a mountain were on display, the whole scene was perhaps four to five meters across, and nearly as high.
"Some description of a religion looks like." Damp Lantern explained, rubbing his chin.
The nest showed another group of figures, apparently imprisoning the first group, with the skull, inside the tomb they were in.
"Oh my...this isn't a tomb. It's a prison." Sandy whispered.
The tunnel ended abruptly, with a great stone door in the way. It was chiseled with beautiful detail, many smaller scenes described around a much larger symbol... The skull from the inscriptions on the wall. With the larger depiction Twilight could see the skull was apparently malformed, and she couldn't quite tell what species the skull belonged to.
"It looks like this door is intended to be opened with magic." Damp said. "Princess, care to do the honors?"
"Gladly." Twilight responded cheerfully. Her horn lit up, and her magic grasped the skull at the center of the door. It hummed quietly.
That was all she could remember before everything went black.
Author's Note
Superesse in tenebris et in umbra eicit adversus eam.
