Shanganagh Castle was opened as a detention centre in 1968 for young male offenders in the 16-21 year age category. The complex consists of the castle, which is mainly the administrative centre, accommodation centre and a block providing education, workshops, gym facilities, etc. Accommodation is provided in a dormitory setting for a maximum of 60 offenders. The regime is open and relaxed with offenders generally receiving 50% remission on the portion of their sentences served there. In addition, offenders are granted periodic weekend temporary release to return home.
The majority of offenders who are transferred to Shanganagh Castle are initially committed to St. Patrick's Institution as this is the main committal institution for young offenders in the 16-21 year age category. Offenders in Shanganagh are generally either first-time offenders or those who are serving their first custodial sentence for a non-violent offence and are not considered aggressive, intimidatory, or to be actively taking hard drugs.