Stormont Castle is home to the Northern Ireland Executive and the Office of the First Minister and deputy First Minister. While it is notable as the building where the Executive meets to agree government policy, it is also a striking piece of architecture with an interesting history.
http://www.niassembly.gov.uk/visit-and-learning/visiting/
http://www.discovernorthernireland.com/Parliament-Buildings-Stormont-Belfast-P3060