I - The Discovery
The green rolling hills of Equestria flew by below the two flying alicorns, recently abdicated from their thrones in Canterlot. Soon green hills turned to white snow, but onwards they flew.
Luna turned to her sister after a while, “Tia, was this really necessary? I get you were bored at the resort, but dragging me along wasn’t very nice.”
“Oh come on Luna, nopony has ever explored what lies beyond the Frozen North, think of the adventure!”
“But we’ve already been on three adventures this week, we have an eternity to gallivanting to the puckered sphincter of nowhere.”
“Equus is big Luna, we won’t run out of places to explore for centuries yet.” Celestia was quiet for a moment before speaking again, “I’ll tell you what, after we get back, I’ll submit myself to another night of that horrendous yowling, I do think it’s slowly growing on me.” Luna rolled her eyes and snorted in agreement.
After passing the Crystal Empire, Mount Everhoof soon came into sight. Veering slightly to go around the cursed mountain and its supernatural winds, they soon found themselves over the Crystal Mountain Range. As the Sun began to hang lower on the horizon, the mountains began to taper away, leading to a flat icy expanse.
“We should find a spot to sleep for the night!” Celestia shouted over the cold wind. Luna nodded and the two broke off to search for a suitable place to sleep. After a few minutes of searching, Luna spotted a small rocky outcropping at the base of the mountains and sent a signal to Celestia. After rejoining her sister, the two headed down and snuggled close together, both for warmth and affection. Casting wards of protection on their location, the two slowly began to drift to sleep.
* * * * *
After waking up, the sisters shook off the snow from their bodies and took flight once more. Leaving behind the Crystal Mountains, they continued their path north, the Sun remaining low in the sky through the day. After long hours of nothing but flat ice, Luna began to grumble.
“Celestia, what do you even expect to find this far north? There’s nothing but frozen plains that stretch on to the horizon in every direction.”
“It’s not what I expect to find Luna, it’s the journey there and the sense of accomplishment on having done it!”
“Well I’m suffering for an accomplishment I didn’t want.”
“Oh lighten up, we’re almost there I think”
Luna grumbled some more but kept up with her sister, if Celestia was bent on finishing this, then Luna would see it done as well.
“What the….” Celestia’s exclamation interrupted Luna’s thoughts and she focused on where her sister was looking on the horizon. She squinted until she saw it too, a collection of protrusions from the ice and snow. The way they were arranged and their shape, it seemed unnatural.
“I see it too, I wonder what it is.”
“We should check it out!” Before Luna could protest, Celestia had already turned towards the strange objects, Luna yelled an obscenity before following her sister.
As the pair got closer, the more the weird shapes began to look like structures. They weren’t of any architectural style Luna was aware of, be it pony or some other race. She caught up with her sister and asked “Do these look familiar to you?”
“No, and that worries me for some reason.”
The two were now flying past a few of the outlying structures, they were brick and mortar, but covered in ice and decrepit. Their bases were buried in the snow and ice, so their true height was a matter of speculation. As they neared the center of the collection, the sighted a far larger structure poking up through the white. Topped with a massive dome and several smaller domes, the structure dwarfed the Castle at Canterlot.
“What on Equus…” Celestia muttered under her breath. She and Luna flew closer to the great structure and soon found a balcony to land on. Being careful on the ancient stones, they looked at each other and nodded, lighting their horns before stepping inside.
They appeared to have stepped into a small room of unknown purpose. There were paintings, books, and scrolls long rotted away, exposed to the elements. They moved to the tall door at the end of the room and tried to opened it, but the door gave and just disintegrated under their touch.
“How old is this place?” Luna asked.
“There’s no telling, I’m certain it’s older than Equestria though.”
The two entered into a dark walkway and gasped at the sight before them. They were standing in a gallery, looking down upon a dark expanse before them. If not for the little bit of light coming from the dome above, they’d have thought they’d stepped into a cavern. The heart of the structure was utterly massive, it could fit almost the entirety of Canterlot Castle in this chamber and still have some room to spare. The floor of the chamber was quite a ways below them, and after a quick look at each other they both jumped and glided down. They reached the floor and looked around. The floor had a coating of snow but the walls held many mosaics. They were too dark to see at this distance so the two split up to check them out.
Luna walked up to one of the many columns holding up the galleries and looked at the incredibly preserved mosaics that wrapped around it. There were depictions of strange creatures apparently in battle with other, more recognizable creatures. Luna’s eyes widened in shock as she saw the clear outlines of dragons and changelings.
Celestia walked to one of the walls and gasped at what she saw.
“Luna!”
Celestia’s cry shook Luna from her focus and she flew over to her sister. “What’s wrong Tia?” She looked at where Tia’s hoof was pointing and she soon shared her sister’s dumbfounded expression. In front of them on the wall was a mosaic depicting three figures. Faust, the Spirit of Harmony and mother to all ponies, doing battle alongside Discord, the Spirit of Chaos. The two were together, fighting against another foe, Grogar, the Father of Monsters.
Celestia soon found the ability to speak again, and she voiced her sister’s thoughts exactly, “What in Tartarus is this place?”