Yes it is hidden. It is in a hutong and has no particular sign outdoor other than the big number showing its address. Ince inside you will find that the staff speak practically no english. This is not a problem as it is a fixed menu. The only decision is whether to drink tea or beer..
There is plenty of food, several types and all very good. This is not a fancy high-end restaurant but a very authentic experience. The good thing about Yunnan food for a westerner is that there is no surprise. This is very accessible food and one of the best value for the money in Beijing.