I recently had a lovely evening here with a Spanish friend. We were lured by the special tapas and wine offer (150RMB for 5 tapas and a bottle of red) which he had tried before. The wine was lovely, however the tapas were significantly smaller than those I am used to back home. Nevertheless, they were very tasty!
I recommend you have dinner before or after (either at the restaurant or somewhere else) as the tapas servings are just not enough to fill you up, especially as you will be sharing with another. The wine and tastefully decorated dining area, however, are enough to put a smile on your face.
I will be back to try some other dishes on the menu and hopefully sample some of the delectable looking desserts I saw in the glass cabinet by the door.
I was surprised I hadn't discovered the Hidden City sooner, especially as I am often in the Sanlitun area. Taught me that I ought to look around a little more often as I tend to frequent old favourites.

I believe the Tapas Special is no longer current, but check it out anyway!