cultural activities
For those who come a few days to Madrid, it is worth having a look to the program of Matadero's activities (see the website). It usually has very interesting urban art exhibitions, as well as music and theatre festivals.
Now it is partially closed due to reforms, but it is very interesting anyway.
excellent concerts
It is worthy having a look once in a while to its program (available in their website). They have great concerts, and there is normally very nice atmosphere. The decoration is not ver nice in my opinion, but it is very appropriate for the occasion.