The standard OBD battleground

The Hyperbolic Time Chamber (精神と時の部屋, Seishin to Toki no Heya; lit. "The Room of Spirit and Time") is a fictional location from Dragon Ball, accessed via Kami's Lookout. Inside the chamber, time seems to pass very slowly, with one year in the chamber being one day on the outside. There is a higher gravity level than Earth's. A step over the threshold of the training area brings one immediately into 10x Earth's gravity (usually ignored in battles), the air gets denser, and the temperature fluctuates the deeper one goes into the training area.

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. Goku explains to Gohan during their visit to the chamber that the air grows increasingly dense in the recesses beyond the plaza, which can be threatening as the Hyperbolic Time Chamber has no definite boundaries. The Hyperbolic Time Chamber represents a separate dimension from that of Earth, which Old Kai called "the dimension of time".

This is usually the default setting for matches in the OBD, should the location not be specified. While a generally neutral area, it lacks materials that many characters rely on for fighting (water, earth, wind, etc.). Often abbreviated as ROSAT.

Also see:

Character Shields
Jobber Aura
Plot Plot No Mi
Plot No Jutsu