Cube/WMG

The Cube series takes place in the Aperture Science Research Facility.

 * The first (purely mechanical) Cube was meant to stress-test potential research subjects. If you escaped with all your marbles, you were sent on to Portal Gun testing. The second Cube (featured in Hypercube) was a parallel experiment, refining the rather bendy physics used by Portal technology.
 * That is totally the kind of thing they would do!
 * But there was no Cake for the person who got out...
 * There wasn't any Cake in the Portal Gun experiment either.
 * There was. The Test Subject just didn't get any.

The two Cubes were developed or discovered by the SCP Foundation.

 * It just seems like something that would interest them.
 * Incidentally, nothing says the above two theories have to be mutually exclusive.
 * Hang on. It's stated that D-Class expendable personell can be taken directly from the public in times of shortage, if there aren't enough Death Row inmates to fill the quota. The characters are newly recruited D-Class, who haven't been formerly initiated since that would destroy the integrity of the test.
 * Hypercube keeps this rolling. The Foundation would definitely be interested in the Hypercube.

The Hypercube is an experimental gateway to parallel universes.

 * The first cube was intended to test the reactions of humans when placed in unintuitive geometries. It proved that humans could, in principle, survive in a highly confusing space-time configuration. This was a precondition to the Hypercube, the actual purpose of the experiment. Assume there are three additional dimensions of time. Construct a singular cube room, place people in it, then rotate it from the spatial into these additional temporal dimensions - but your parallel-universe equivalents are doing the same thing, thus resulting in an infinite lattice of cubes in six now-spatial directions, joined at their entries/exits. But .. time isn't that neat. Maybe one of the parallel universes switched their cube on a microsecond later, maybe the atmosphere has a different composition, maybe some natural constant is subtly different - the rooms aren't traps, they're flaws in the lattice.

There is nothing outside the Cube.
The Cube is the only real thing. The memories of being in the real world are false. The prisoners were vat grown. When you go outside, you die almost immediately. Hypercube is another dimension.

The Cube is in space.
All survivors are shot out the airlock immediately. If they're particularly unlucky, they may have to listen to some poetry first.

The Hypercube is a failed attempt to recreate a TARDIS.
Just think about it. It's bigger on the inside, can manipulate space, time, gravity, etc. Some time ago, humans might have acquired a broken TARDIS and then built something that was supposed to resemble it. They failed.

Each room of the Hypercube has six interiors at a time.
The rooms rotate in three spacial dimensions; what's to say they don't rotate in four? This is how, before, some marked rooms seemed to contain variable contents. Whether the interiors each belong to one of six different internally consistent sets (forming the "parallel universes") or if each room has its own set of six interiors depends on how the cube was made. has fewer than six of each kill trophy, so it could be either. If each room has more than 6^1 interiors, that really doesn't add any meaning to this guess other than narrowing down the possibilities of how the cube was unfolded/folded/formed/whatever. Obviously, this doesn't include the limited external room[s], since.