Submission for the 2013 Nightmare Night fanfic event.

Don't walk into the woods...

The carnival arrives without warning. No announcements precede it, it is simply there, arriving with the bombastic overture of spells, contraptions, and performances, as intricate as they are spectacular.

It isn't long before ponyville- and it's heroines- become involved... and all too soon, things seem to look strange. A great number of patrons, none of which seem familiar even in Equestria... A sudden upheaval that could threaten not just the carnival, but anything beyond... And a power, something great and arcane and incredibly ancient, that sits at the center of it all...

Somewhere below the sea, there lies a city.
A city envisioned to be the home of invention, of progress, where the finest minds of all of ponykind would be allowed free-reign, and so reach a potential undreamt of on the surface.

Yet something has gone terribly, terribly wrong, both with the city itself and it's inhabitants. Now, only abominations and the keening wails of the damned inhabit the once bustling tunnels and domes of that great place, and of all thats left of it's former splendor there is only rot and rust.

Is it possible to escape such a nightmare? Is it at all possible for an individual to survive such horrors, such insanity, without being tainted themselves?

Perhaps that is the only fate that await those inside; to die under the waves, alone and forgotten... or to leave a monster.