The capital of Northern Ireland, Belfast is perhaps best known for being the birthplace of the RMS Titanic (whose history you can explore at the Titanic Belfast museum). Beyond its history for building sunken ships, however, Belfast has become a true destination city in recent years, with sweeping sea views, a wealth of museums and galleries (including the Ulster Museum, located in Belfast's botanical gardens), and a lively bar and pub scene in Cathedral Quarter.
If you'd like to explore the lands of Gaelic mythology (and Game of Thrones) on your Northern Irish adventure, rent a car and drive about an hour north to Giant's Causeway — a collection of stacked basalt columns that, legend has it, were once a causeway constructed by a giant named Fionn mac Cumhaill.