This hotel is excellent. The hosts were super friendly and there for us (bringing us home-made snacks as gifts, driving us places when we needed it, giving us a free upgrade because it was a bit slow when we were there, the list goes on!).
The place is <5m walk to an amazing pork restaurant, the excellent Joanne Bear museum, the very hip and beautiful Vadada lounge, about 5 sushimi places at Daepo Port, and a bus stop for the airport, <10 min walk to a cliff side path and Jusangjeolli cliffs park,<25 min walk to the ICC and to groceries, restaurants, and booze in Jungmun-dong, and <40 min walk to Jungmun Beach and Cheonjeyeon Falls. Take the bus from Jungmun up Mt. Halla, its beautiful.
The rooms are beautiful, clean, well-stocked, serene, and have beautiful views. We had five nights in Jeju in mid-June, spent all of them at Sunnyday, and had a beautiful time. HIGHLY RECOMMENDED.