I visited Belfast on a work assignment recently and agree that it's difficult to get there from overseas. Belfast's two airports are small and mostly served by regional airlines. I chose to fly in to LHR on my trip because I needed to visit a few sites in the UK and Northern Ireland. I used trains, buses, and regional airlines to travel between smaller cities. If I were visiting only Belfast I would probably fly to Dublin and take a bus to Belfast. Bus services run nonstop from DUB airport to Belfast downtown approximately hourly throughout the day at a cost of somewhere around $20 US. It's an easy, 2 hour ride.