We had a great time at Christian and Katie's! The flat is at a prime location, right by the Royal Mile in the old part of the city and 5 min from the train station by foot. Since no other guests were staying the night before us, we were able to check in early on Saturday morning, which greatly facilitated our arrival. The flat was great for 2 couples. It was clean, comfy, and we quickly felt at home. We had some issues with the heating in the living room on our first day (due to an odd combination of switches), but this was resolved quickly, and Katie had already offered to buy a space heater in the meantime (she was also very prompt to answer all of our messages). The street can get a bit noisy during the evening (there are a couple of pubs) but the bedrooms are insulated enough so that it didn't prevent us from sleeping. The mattress is the main bedroom is a bit soft, but this is a minor issue. In conclusion, we definitely recommend the Royal Mile Refuge for a stay in Edinburgh (which is a great city!).