There is no reception or service at this hotel. There is a restaurant downstairs, but it was closed during our stay. They simply send you a code for self check-in. Make sure to double-check your room, as they initially gave us a different room from the one we booked, though they changed it quickly after we contacted them.
One tip — visit Kirkjufellsfoss early in the morning. There is almost nobody there, and you can enjoy the whole mountain completely to yourself.