Up to 116 males, five females and four families can be held at Tinsley House detention centre, a rather anonymous looking building near Gatwick Airport
The purpose built immigration centre was opened more than 12 years ago. Visitors are allowed to see detainees between 1400 and 2100 GMT each day.
Staff at the centre say they try and process new arrivals as quickly and compassionately as possible to make their experience less traumatic.
Family groups are housed in a separate area away from the single detainees. The UK Border Agency says it aims to keep them at Tinsley House no longer than 72 hours.
Many people kept at Tinsley House have been stopped by immigration officials at Gatwick Airport but the centre also takes people from Heathrow and Luton airports and ports such as Dover.
Staff at the centre say the facility is similar to student accommodation and they try to foster a family atmosphere to make the detainees' stay as pleasant as possible.
However in August the Chief Inspector of Prisons, Anne Owers, said conditions at Tinsley House were "unacceptable" for a small number of women staying there.
The centre is equipped with a gym, computer room, chapel and library. Detainees are also encouraged to take part in art and craft workshops.
Security at the centre is obviously high, however the staff emphasise that Tinsley is not a prison and detainees are never locked in their bedrooms.
Campaign groups that have protested against the new 420-bed centre due to open in march believe "administrative detention" is a violation of human rights.