Prison Planet

The Prison Planet is a set of seven planets chained together and used as a prison by Fu.

Planet description
One of the planets resembles real world Earth, another resembles Saturn, one planet is mechanized (like the planets of Universe 3) while another appears to be made almost entirely out of lava. The planets are tied together by massive chains, with a keyhole being present at the center.

One of the planets that makes up the Prison Planet is Babari from Universe 10, which is the planet where Fu has set up a prison, and where Future Trunks has been imprisoned.

The planet contains it's own set of Dragon Balls, simply referred to as "Special Dragon Balls" by Fu, which are needed to leave the planet.

History
The Prison Planet was created by Fu in the second version of the future timeline where Future Trunks lives after the "Future" Trunks Saga as an experimental site[3] and also as a prison, numerous warriors from across time and space were imprisoned here as part of Fu's experiment.