Berlin underground library
Patrik Ward from Readhacker linked to my photo. And please check his web site: it is a pretty neat one, with all the needed features for mobile devices.
Web 3.0 anyone?
After a little research on the subject I discovered that at some point books were visible on the shelves, as one can see in this other photo by canonsnapper.
Personally, I think the empty shelves are much more effective.
For people interested in the argument, here you find the relevant Wikipedia article. Quite interesting, especially if seen in the light of the recent try to censor the Internet. Learn from history.