You may have seen the flash mob performing the Ode to Joy from Beethoven's Ninth Symphony in the Plaza San Roc in Sabadell, Catalonia (in Spain). If you haven't, you can find it here, and it's definitely worth seeing, both for the performance and the delighted reactions of the people present.
Here's a similar performance at a shopping mall in Tokyo:
And here's another in Nuremberg.
The Ninth Symphony is so popular in Japan that it's often just called "Number Nine." Performances on New Year's Day have become traditional. A truly remarkable one takes place in Osaka with one of the largest choruses ever assembled. See this link.