Spike opened the door, certain that he had finally found her. But what he saw as he looked around the room ...
The first thing he saw was the ladders, very precariously balanced like they might collapse on some pony trying to climb them. Then the ropes above a pit of spikes. Everywhere he looked, dangerous, unsafe setups, even what looked like a giant pendulum barely held back by little more than a stick with a rope attached to it. And that rope itself was attached to a trip-wire on the obstacle course.
Spike was suddenly distracted by the sound of clopping hooves, thundering in the air above him. Looking up, Spike saw Twilight running up the wall, flapping her wings to hold her on the wall, while clearly pushing hard with her rear legs. Right after wondering why she was running up a wall instead of flying, he realized that not only was it faster, but --
With a loud "wham", several spiked objects embedded themselves in the wall right behind Twilight as she ran up. Spike realized immediately that if she had been flying, with its slower ascent, she would have been hit.
"Twilight!", Spike yelled. Distracted by the unexpected sound of her assistant, Twilight missed a step, and faltered a little.
"Spike!?", replied Twilight, as she realized her misstep, and put a shield up around her. With several "thumps", the last of the projectiles bounced off her magical shield, harmlessly to the ground.
With a couple of flaps to hover in the air, Twilight looked around, and proceeded to aim her horn at various devices, turning them off. Gliding down, she landed next to her loyal assistant.
"Spike, what are you doing here? This place is not safe for normal ponies or dragons. You could get hurt badly here," she said, with concern for her loyal assistant.
"Me? What about you? This place is ...", as he glanced around the room, seeing all the various contraptions, everything ready to fall over with a slight error in usage, etc. "This room is just full of danger. What are you doing?"
"I'm practicing," Twilight replied. "It's not that dangerous for an Alicorn, but I still need to practice my skills. I figured that if I could make a secret training spot, I could practice my skills, and improve, without anyone ever noticing or getting worried about me". She was not quite ready to reveal the source of inspiration for this idea.
"With no one to act as a spotter in case of a problem?". Spike was very concerned about Twilight’s behavior here. "If something happened and you got hurt, who would know? Do you realize how reckless and irresponsible this could be? Who is going to look out for you?"
With a sigh, Twilight looked at him, and lowered her head a little. "You may be right, Spike. I should have told someone." With a smile on her face, she continued. "So now I'm telling you. Have you ever dreamed of being a Power Pony?" Indeed, the concept of super ponies, training in secret danger rooms, had been the core concept that inspired this place.
Spike looked around. Looked at Twilight. Looked at her eyes, and how she was behaving.
"Are you insane!? Twilight, do you have any idea how ...". One more look at the unicorn that he had grown up with, now an Alicorn, and realized just how much she had changed. "How overpowered you already are and don't actually NEED this?"
"But it's not the same if I just toss magic at things. I've been doing that forever. Half of this course is intended to improve my earth pony abilities. Half is for my pegasus flight and maneuvering. Heck, that wall I was just on requires both of them together. If I'm not prepared to push myself, how will I be a better student? How will I be a better teacher to my own students?"
Spike realized that he had no answer. As crazy as Twilight could get at times, she had a good point. Yet the idea of her doing something that could injure herself made him worried, concerned, and --
"Power Pony?" he asked, with the thought of his comic books,
"Like Mare-do-Well. I see myself in a black cape, covering all my distinctive features, so no one will be able to tell --"
"Wings. Horn."
"Err, well, I figured an illusion spell would --"
"Half of the unicorns in Canterlot. Heck, Trixie or Starlight would see through that in an instant. Seriously, it would be the most obvious, badly kept secret unless you were to go halfway across Equestria. Even then it would be a matter of time. The only way you could keep this a secret at all would be to go out into other lands where every creature doesn't know about the types of ponies, and even then you'd have to hide at least part of who you are."
"I’m already prepared to hide that, as I said, I can put an illusion up to hide one or the other. Heck, the locals will think that there’s two of us. No creature will ever make the connection."
Spike looked at her, as she was saying this. Suddenly, realization dawned. "Did Celestia put you up to this? Is she going to use you as some sort of agent in remote lands?"
"Luna, actually."
"Luna? Seriously?"
"Apparently, she says that this is something that I've dreamed about, and that I would be good at." Twilight smiled at Spike, and then said, "You know, any good super pony has a sidekick."
"Me?". Spike gave this a thought, and then said, "Someone has to keep you safe from whatever danger you're going to get into. Alright, let's do this."
"So let's get dangerous, together!"
Later, in another city, on a dark night, two winged figures dressed in black were seen.
"We are the terrors, that flap in the night!
We are the defenders of all that is right!
We are Dark Wings tough!"