Dublin Castle

The former seat of British rule
Word to the wise: One of the city's most appealing cafes, Queen of Tarts, is situated right opposite the castle gates on Dame Street.

It must be pointed out that if you are looking for an old, fairytale castle in the moats-and-turrets sense, Dublin Castle will disappoint. Rather, it's a cluster of historical buildings, some dating from medieval times, which are now primarily used as government offices.
It may not sound thrilling, but there's lots here for those interested in Irish history. For centuries this was the seat of British administration, serving variously as a prison, the law courts, and the city treasury. Unsurprisingly, it was besieged during the Easter Rising and, in 1922, was handed over to Michael Collins and the new Irish Free State Government.

Visitors can view the two 13th-century towers, the beautifully decorated state apartments, and the neo-gothic Chapel Royal - alternatively, just wander around the grounds for free or head straight for the wonderful Chester Beatty Library. During the summer months, the castle hosts arts festivals and concerts.