The star system Omega Centauri was just another oddity on a map to scientists in the not too distant future. However when they found the star was orbiting an earth-sized, earth-like planet instead of a black hole as its motion had suggested, a mission was scrambled to investigate this most unusual of celestial behaviors.

Hamstrung by politics, and nearly crippled before it began, the 'Lone Ranger' mission was reduced to just one crew member and left to his own devices.

These are the logs of Arrow 18 and its lone commander. This information is classified TOP SECRET by the Global Space Agency.

Do NOT tell the princess.

Princess Celestia tires of constantly being surrounded by decorum, deference, and formality, and decides to take a day off from being Princess. But visiting Ponyville incognito is harder than she expects. Will she be able to fit in and make friends without blowing her cover?

What started as a normal friendly visit ends up taking two ponies on a trip down memory lane that leads them both to realize their friendship began even before Rainbow Dash's first sonic rainboom.

The Shaper is a smith of unparalleled skill, her creations the most sought after in the fallen world. When a pony named Lyra comes to her with a unique commission she has to put all her skill to the test to craft a weapon of great power. For Lyra's goal is not an easy one, and it is not just any weapon that can kill a Dragon.

A story inspired by this and this image, as well as this challenge by CDRW (whose fic A Still More Glorious Dawn Awaits is quite good).

Isolated from her friends and taken prisoner in the middle of a war, Twilight must deal with the very real dangers of being percieved as an enemy as well as the nightmares of her arrival on 'Earth'. Can she overcome her own fears and the fears of her captors? Will the wayward unicorn's assistance be a boon or a curse to the 'humans?' Most importantly, will she ever find her way home?

"In short, it's a story of friendship and plasma rifles, with the emphasis on the friendship. The characters are well written, the XCOM setting is fleshed out very well, and the story is compelling. If you love XCOM, you'll love the story, but even if you've never heard of it, it's more than worth giving the first 3 chapters a read.

There's excellent action later on, but the real strength lies in the collision between the friendly and naive world of Twilight Sparkle and the desperate world of humans fighting a losing war for survival and willing to do anything to turn the tide."

--Arzoo

(XCOM/FiM crossover)
(Cover art commissioned by a friend and created by the magnificent FoxInShadow!)
(Original cover art by the amazing Carnelian can be viewed here!)
(Gore tag for blood and some violence)
(Many thanks to the studius OminousTen, Arzoo, xXFluttershyForeverXx and finally Setokaiva for giving my rambles a once-over)
(Now with it's own TV Tropes page! Get to tropin' folks!)

Ever since moving to Ponyville, Twilight has neglected something: her other residence. The rooms she used in the Canterlot Archives are still filled with her possessions. It's been nearly a year, and the Archives want her to clear out already so the place can go to the new departmental librarian. She has until sunset -- or anything still there just might remain so. Spike, knowing the deadline is hours away from arriving, recruits the Bearers to help her.

But Twilight doesn't want help.

A deadline is in front of her, and she's -- stalling.

They have until sunset...

(Part of the Triptych Continuum, which has its own TVTropes page and FIMFiction group. New members and trope edits welcome.)

Now with author Patreon and Ko-Fi pages.

North of Canterlot, in the far marches of Equestria near the border with the Griffon tribes, there is a mountain that flies.

West of Canterlot, beyond the Galloping Mountains and a desert painted in the pastel hues of a faded rainbow, a tower sits at the edge of the world.

South of Canterlot, past the Everfree forest and the desolate badlands, a city of gardens waits to be born.

The Lost Cities Challenge! Awesome authors who have taken it upon themselves to explore other abandoned places:

- The Land of Glass and Stone, by RazgrizS57
- The City that Breathes, by Pearple Prose
- Aletheia, by Foehn
- Far Kobresia, by Baal Bunny
- Keskiyönnon, by Bradel
- Unknown Architecture, by Not_A_Hat
- The Gentle People, by Bad Horse
- The Seal of Wax and Glass, by DuncanR

Dramatic Reading by Illya Leonov: Chapter 1, Chapter 2, Chapter 3, Chapter 4.

Royal Canterlot Library interview for Lost Cities.

Early one morning, Twilight Sparkle gets up to make some tea.

Sometimes, a cup of tea is just a cup of tea. This is not one of those times.

When Twilight Sparkle slipped beneath the covers last night, everything had been fine. She had friends whom she loved, a teacher she adored, and a bright future ahead of her. But when she woke up, her blankets and quilts had been replaced by hospital gowns and padded restraints.

Everything is wrong and nothing makes sense; even her friends have changed. The doctors keep telling her that she is sick, that none of it was real and that it was all in her head. Yet she remembers a life far beyond the hospital walls. She couldn't have made it all up on her own. They must be lying… right?

Ask Asylum Twilight - Still updating regularly!
Equestria Daily
TVTropes
Asylum Fan Group
The Tartarus Project
Russian Translation
The Asylum 20,000 View Spectacular Stage Show!

Art:
Asylum Cover by conicer
Twilight and Twilight Smiles by dreamingnoctis
Mirror Twilight and Plague Doctor by Jaestring / BloodGoldWings
Twilight Smiles and Doctor AJ by conicer
Nurse Ratchet and Silas and What's in the mirror? by Archonix
Doctor AJ Sketch by Archonix | Colored and vectored version by ReFro82
Twilight's Asylum by Khan the Cake Lover
Smilight by HappySwitch
Twilight Waking Up by Dombrus
Fan Art by toxicdemon10
Asylum Twilight by Madness-With-Reason
Asylum Fluttershy and Asylum Ch 26 by Downburst-Backspace
Twilight and her Twin by v747
Birdgirl by sirValter

Readings and Videos:
Asylum Animated Trailer Video by formuladash
Reading by Gammarobot (SugarCubeRadio): All Chapters Here
Reading by Ender Brony: All Chapters Here
Reading by VisualPony: All Chapters Here
Reading by MelancholyIguana: All Chapters Here
Fan Trailer by Kaidan: Asylum FanFic Trailer Cuckoo's Nest

Sanctuary by Kaidan
Broadhoof Files: Dr. Humors by TypewriterError
Broadhoof Files: Corporal Phalanx Spear (Ret.) by Phalanx Spear
A Hearth's Warming Tragedy by Seven Fates

A special thanks to Breath of Plagues, Rex Ivan,
ChudoJogurt, Cynewulf, Death the Kid, Selbi, PrinceDolph, Blahman2816, Queue, and Gage!

Axan Zenith - Dr. Dreamer
Dratini4 - Way Finder
psychicscubadiver - Bright Mind
Velkaden - Dream Chaser
Reese - Silver Glow
Viola Heartstrings - Clover
Archonix - Spinney Whiteacre

After a magical accident, Celestia and Luna must try to restore harmony. Celestia's duplicate, however, is having none of it.

Check out the companion pieces, Amphelion, by monokeras and The Banach-Tarski Dragon by CCC, tackling the same premise in a different way.

Cover art from the gallery of mysticalpha.