The ferry from Incheon to Yantai took 15 hours and was really awesome mix between container and pessenger ship. The pessenger part had probably some years ago some awesome comfortable environment, but these days its all old and damaged.
Specialy the other guests where an great experience for me. There where hundreds of chinese around with >50kg luggage each person with all kind of Korean technology parts. I am pretty sure i was the only western on the hole Ship.