Carrickfergus Castle, located in Northern Ireland, was built by John de Courcy in 1177 and played a significant military role until 1928. The castle has a rich history of being besieged by various forces, including the Scottish, rebel Irish, English, and French. It is one of the best-preserved medieval structures in Northern Ireland, offering visitors a glimpse into medieval life with exhibits and a restored banqueting hall. Today, it is maintained as a historic monument by the Department for Communities and remains open to the public for exploration and learning about its fascinating past.