Kilmainham Gaol is one of Ireland's most popular visitor attractions, although 'attraction' hardly seems the most appropriate word.
Most jails it seems start out based on fine principles and slowly degenerated into squalor and overcrowding. In Kilmainham's case this happened twice.
The original building, now known as the West Wing, was built in 1796 according to the latest Howardian principles to replace the nearby 'noisome dungeon' used up to that date.
The East Wing was added by the Victorians in 1864, and was built to the latest 'panopticon' design. Interestingly, whilst the old West Wing was designed to keep prisoners in the dark as a punishment for their misdeeds, the East Wing was designed to flood them with light and keep them looking upwards to God.
It closed to general prisoners early in the twentieth century, but was reopened by the British to house the leaders of the 1916 Easter Rising, most of whom were executed by firing squad in the Stone Breakers Yard.
It continued to be used for political prisoners throughout the War of Independence and the subsequent Civil War, before finally closing in 1924, its last prisoner being Éamon de Valera later to become Ireland's Taoiseach and third president.
Entry to the main jail is by guided tour only, but there is a large and fascinating museum to keep you occupied while you wait. For full details of opening times etc. please see the Heritage Ireland site detailed below.
In addition to the bus routes detailed on that site, it is also served by the hop-on-hop-off sightseeing buses, and is about half a mile (900m) from the Luas Red Line Suir Road tram stop.