"There are no 'windows,' per se, but your suggestion is very similar to what we had planned for you."
A 3D map pops up. It displays a large, heavily fortified facility. Most of the facility is underground. Numerous guard patrols are outlined along the structure's perimeter and on its exterior. Large cannons, probably designed for use against orbital targets, are mounted on and around the building. A thick wall, shielded and topped with razor wire, surrounds the area, and has only a single gate, which is guarded by dozens of soldiers. The main building itself has three doors, one facing north, one facing the gate in the west, and one facing south. Each is well guarded. There are no windows, and not even any ventilation apertures.
"Apart from the doors, which I'm sure you see are impregnable, there is only one way in."
The holo zooms in, showing a large, oval opening near the top of the building. There are a few guards stationed around it.
"That opening provides ventilation for the entire building. It is the one weak point in the defense. It's really rather sloppily guarded, and there's a reason for that: it is extremely dangerous. The intake is heavily filtered, so going through it would be suicide. The outlet is very high pressure, so keeping your feet would be tough enough. Throw in the fact that they vent toxic, superheated exhaust through there, and it appears to be equally deadly. Just for good measure, the freakin' paranoids went ahead and put the only automated defenses in the whole facility in the outlet tube, as well."
The holo shuts down.
"As you can see, it's not a one-man job. However, the plan you outlined is almost exactly what I had in mind, though the window involved is a bit unconventional."
He smiles and steeples his fingers. "I see you are somewhat familiar with Fictionite. It comes in many different varieties, but most share a great deal of properties. Probably the most famous and widespread type of Fictionite is Adamantine or Adamantium. Mithril is also pretty famous. Then there's neosteel, Valyrian steel, blacksteel, durasteel, and such. Some are more durable and valuable than others within their own worlds, but outside their home dimension they are usually all about the same strength. It has something to do with detachment from their own universe's magnetic fields. It is also known, though, that Fictionite is more powerful in an alloy. The more types that are alloyed together, the stronger (and more valuable) the Fictionite as a whole becomes."
A hologram of a suit of light power armor appears over the table.
"This is the standard power armor our security forces use. It is made of Neosteel, one of the weaker varieties of Fictionite. Not too valuable by itself, but if we secured some other type of Fictionite to combine it with..."