Designed by Messrs Hansom and Welch of York and constructed in 1829, the gaol is situated near the centre of the town of Beaumaris. With its high stone walls and this heavily secured entrance, this cubic structure is surrounded by an air of gloom and foreboding. The interior retains the same somber mood. On two floors, long dark corridors lead to the cells and workrooms and iron bars separate each wing.

Gas lighting was installed in the gaol in 1857 and a water supply system powered by a human treadwheel came into operation in 1867. The atmosphere within the new wing, which was added to the prison in 1867, is different from the older wings. It reflects the change from the Silent System (in which inmates were forbidden from communicating with each other) to the Separate System (in which inmates were isolated). Imprisonment also involved hard labour, the intensity of which depended on the crime which had been committed.

The building was used as used as a county gaol between 1829 and 1878. In 1877, prisons transferred from the county authorities to the central government, and Beaumaris Gaol was closed and its five prisoners were transferred to Caernarfon. The gaol was a police station until 1952 and it opened as a museum of prison life in 1975.