Ashtown Castle is a tower house in the Phoenix Park in Dublin, Ireland. It was found hidden within the walls of a much larger and more recent Georgian building, the Under Secretary's Lodge also known as Ashtown Lodge, that was being used by the Papal Nuncio until 1978. At that time, the Lodge was deemed structurally irreparable due to dry rot. However, as the building was being demolished, Ashtown Castle was discovered.