I just returned from my first visit to Seoul and stayed at the D Cube - I could not recommend it higher. Fantastic rooms, service is excellent. Easy to reach from Incheon and Gimpo via public transport with the subway right under the hotel which makes getting around the city really simple. The fitness facility is the best I've seen in any hotel and some super spa treatments if that interests you. I would not hesitate to stay there next time I'm in Seoul.