Humans.

Truth or myth? Ancient lost civilization or just an old pony's tale?

No pony has ever seen one, and most haven't even heard of them. But Lyra knows that these wonderful creatures are more than just old legends, and she's going to find out... and possibly drive her roommate insane in the process.

The Princesses find an alien creature barely clinging to life at the scene of a terrifying crash. Can the Combined Power of the Elements of Harmony save it, or more importantly, should they save it? Will the arrival of this strange creature tear Equestria apart?

TV Tropes
https://tvtropes.org/pmwiki/pmwiki.php/FanFic/Article2

Rainbow Dash struggles to figure out why Pinkie Pie keeps acting weird, and seems so happy about spending Hearts and Hooves with hanging out with her, while also puzzling over the fact that Cloud Kicker and Blossomforth seem to be going out of their way to help the two of them enjoy the day.

Cloud Kicker and Blossomforth need to have their own tags, because they're awesome characters who deserve to have more stories written about them.

Has a semi-sequel-follow-up-side-story:"The Life and Times of a Winning Pony."

Chris and Keon are two zoology majors that get separated from their class after following what Chris believed to be an undiscovered species of bird, during a trip into the Amazon rainforest.

Finding themselves stuck in a pit, they discover an ancient ruin adorned with murals and statues of what they believed to be ponies. They soon realize that the bird in question was the orchestrator of their fate, as they’re brought to what they are certain is their deaths.

Waking up, they are not only separated from each other, but in a new land entirely. Will they take this opportunity to learn about creatures only ever seen in legend, or will they be too busy being studied themselves?

Rated teen for sexual themes, crude humor, mild drug use.
(Edited by DF)

A slightly more realistic take on the "Human in Equestria" story concept.

... For a given value of "realistic."

Okay, it's barely realistic but it is a hell of a lot of fun...

Now with an image graciously provided by Page Turner, and an audiobook version narrated by multifanficaday and if you prefer it in German, FrankyDoodle has got you covered!

And a TVTropes Page!

Last Featured: 11/26/2019! Thank you so much!

"Who are you?!"

Lyra wrenched her hands together, strands of teal hair falling over her golden eyes. Suddenly, she seemed so small. She didn't answer. Couldn't? It hurt to remember, hurt to say. She was lying, or maybe it was the truth, and she really didn't know.

Cover art done by the amazing Conicer and bunnish!

The Canterlot Caverns are a strange and enigmatic place, untouched and forgotten by pony-kind for centuries. So when a strange metal object is unearthed in their depths, it's up to Twilight Sparkle and Lyra Heartstrings to discover the many secrets it holds.

Together, the two of them will have to do their best to understand the remnants of an ancient civilization, and decipher what remains of Those Who Came Before.

The cover-image is a cleverly edited stock image, which was modified by the stupendous Corvo.
Proofreading was performed by the equally fantastical writers:
Timetraveling Pony (Who started as a proofreader when Cloud was writing this. Hats off to him for being dedicated and staying on as a proofreader for me.)
DustyPwny
Tidal
Superluminous
Night Spark
PhiliChez

And a special Thank You goes to The Sentient Cloud for allowing me the honor of continuing this great story after he retired from writing fimfictions.

As it turns out, this story is eerily similar to Lyra Heartstrings and the Hand of Man. Due to their similarity, I feel that it would be appropriate to give said story a mention.