Info and Rules.

The Hyperbolic Time Chamber has an entrance at its center, located in a central building with two side wings with housing, food supplies, bathing quarters and sleeping quarters. There is no night or day in the Room, but the surroundings remain a constant bright iridescent white aurora. Its reflective floor is of undefined area, and the Room's boundaries are thought to stretch to infinity in all directions even though it appears to have a definite atmosphere, limiting its size. The Hyperbolic Time Chamber represents a separate dimension from that of Earth.

The time dilation that occurs in the Hyperbolic Time Chamber is one day of real time is equivalent to one year in the Chamber, or 1 second of real time is approximately six minutes in the Chamber. There are dual giant hourglasses of emerald sand adorning the sides of the building that count down a year within the chamber. A clock on the dome roof of the main part of the building tells the applicable time in the real world.

This essentially allows for someone entering the Hyperbolic Time Chamber to get one year worth of intense training in a single day.

The gravity in the Hyperbolic Time Chamber starts at 1 g at its center and increases proportionally to the distance away from the center (i.e. as one moves further away from the Chamber's center, the gravity one feels increases). Goku, Gohan, Vegeta and Mirai Trunks are the only characters shown to go deep into the chamber. It isn't shown if Piccolo, Goten, or Trunks did, though it can be assumed at least Piccolo could do that.

The wooden door entrance is a portal between the Earth and the Hyperbolic Time Chamber, and is the only way to travel between the two dimensions without ripping holes in the dimensional walls.

The Chamber can only be entered twice by a person, as by the third time the door locks, leaving them in nothingness and not allowing anyone else to use the door. Also, there are only enough provisions to accommodate two people for the full year. This is commonly misinterpreted as a two-person limit overall, but it should be noted that in the Buu Saga four people in total entered through the main door.