In May, given it's name it couldn't really be at any other time, there are a series of events aimed at showcasing the talents of young people. It's called Much More May (the alliteration works in English as well as Spanish.) As a small part of the event on the 15th Museums and other cultural attractions in the City are going to open for free from 9 in the evening till 1 in the morning.
The youth service people are looking for volunteers to work in the museums for the evening and to "adopt" one of the exhibits or pieces from the various museums so that they are on hand to give visitors detailed and specific information about the "life and miracles" of each piece.
If I'm not too old I quite fancy volunteering. I'm often heard to complain about the lack of innovation in Spanish museums so it only seems reasonable to give a hand when they do show a bit of zing. Though, strolling from museum to museum on a warm May evening and stopping off at an occasional bar sounds good too.