As hallways go, it's of the typical non-descript variety. Off-white walls broken up by other hallways intersecting at 90 degrees and off-white doors that are labelled on the wall next to it with a small black plaque embossed with eight digit numbers in a simple white font. If it wasn't for the helpful arrow signs with the same plain white font on black background pointing to stairwells, offices and special rooms, one would quickly become lost in the seemingly endless maze. While the hallways themselves seemed to be devoid of life, a hubbub of multiple voices and the thump-thump of loud music could be heard echoing down from some unseen location.
However if a casual observer was present in that hallway, he might notice that one of the walls had an unusual quality about it. Careful scrutiny of the wall might show it shimmering ever so slightly with an almost imperceptible undulation much like the still water of a calm pond. If one were to put one's hand on it, it would feel like a normal wall, solid, unmoving, yet further viewing would show that your own hand now showed the same effects that you saw with the wall.
Soon though the slight undulation gives way to very visible ripples caused from a pressure wave preceding an approaching object. Within a fraction of a second there is a flash of light as a yellow pegasus named Fluttershy comes flying out of the wall screaming in terror only to have it cut short as she hits the far wall and crumpling to the ground, stunned from the impact.
Within a second another pegasus with a blue hide, rainbow coloured mane and tail, and aptly named Rainbow Dash followed. Dash manages to avoid the wall, but instead of turning safely to the left or right, she chooses up, and smashes into the ceiling. She crumples in a heap on top of the still prone Fluttershy.
Three more equines come running through the portal, a regular orange coloured earth pony named Applejack, and two unicorns, the purple coloured Twilight Sparkle and the white Rarity. The last one to cross the threshold was a pink earth pony named, appropriately enough, Pinkie Pie, hopping on all four hoofs like some deranged oversized Easter Bunny.
The four pursuers stop dead with the realization they have entered a strange new environment, their fallen comrades temporarily forgotten. Even the normally unflappable Pinkie Pie could only stare slack-jawed, though it may have more to do with having transferred from the chaotic and often scary and dangerous, thus fun environment of Equestria's Everfree Forest to the orderly and apparently safe, thus boring environment of the non-descript hallway.
The stunned Fluttershy stirred, managed to shift Rainbow Dash off of her and shakily got to her feet. "Where are we?" she asked groggily.
"We seem to have yet again crossed a threshold to a parallel universe," observed Twilight in an almost clinical fashion.
Fluttershy let out a little squeak of terror before repeating the word 'no' in rapid succession. Before any of her friends could intervene she flew directly into the wall they just came out of only to once again find an unyielding barrier. Again she crumpled to the ground stunned, fortunate though that she didn't have the same built up momentum she had when she first traversed the portal.
Rarity looked down at her fallen yellow friend with sympathetic eyes, "Fluttershy dear, you know those portals only go one way. We'll have to look for the return portal in another place."
"Speaking of which, Twilight," interjected Applejack with her characteristic country drawl and a heavy dose of annoyance, "I thought you said you knew where all the portals were and how to avoid them."
Twilight winced at the criticism, but had a ready answer, "This one came out of nowhere. Still, we could have avoided this one had Fluttershy not flown straight into it."
"I couldn't help it. I..saw…something…this…thing. It had big red glowing eyes and huge fangs," whimpered Fluttershy, giving a little shudder at the memory.
"It was a snail. I saw it." It was Dash having regained her senses and was now propping her head up on one hoof.
Applejack nodded in understanding, "Knowing the Everfree forest like I do, I would say both are likely true."
"Regardless of how we got here," interposed Twilight, "we need to find a way back so we can complete our mission."
"What in tarnation?" The loud exclamation came from Applejack. She had approached a nearby door and was pawing at the door knob with her hoofs and then attempting to turn it with her teeth, both to no avail. "What sadistic creatures would create round door handles?"
"Creatures with hands," hypothesised Twilight.
Applejack gave a perplexed look and Rarity spoke up echoing the orange pony's confusion, "I thought you said 'hands' were an ancient form of unicorn measurement?"
"It is. It's what is known as a homonym, same word, different meaning. In this case it refers to the appendage at the end of forearms of certain primates such as monkeys and apes and other bipeds such as minotaurs. They are similar to dragon claws but without the sharp nails on the end," Twilight paused, her horn glowing as she magically studied the door, "Hmmm, judging from the size and shape of the door and placement of the handle, the creatures that built this are likely giant bipeds, about the same size as minotaurs. Anyway the door is locked."
"Can you unlock it?" asked Applejack.
"I can, but I don't think I should. It's probably locked for a good reason, and we need to get the lay of the land before we start going into places we're not supposed to. At least these signs are written in equestrian, which should help."
Before they could explore any further, Twilight felt the familiar tingle of another portal forming. She glanced down the hallway and could see the ripple effect being produced on another wall some 20 feet away, but before she could move another being stumbled through the portal. He was tall, wearing green leather clothing and his face was mostly obscured by a green hood. He carried an archer's bow and a quiver half full of arrows on his back. The being looked around in alarm at his surroundings before catching sight of the ponies. The stranger pulled out an arrow and notched it in his bow with an astonishing speed and skill that surprised Twilight. With the other ponies now aware of the stranger, they collectively let out a scream as they become conscious of the mortal danger they are now in.