Open House is one of the most important global institutions for the promotion of architecture. The idea began at London in 1992 and until today it has spread to many cities around the globe. The Open House project invites the public to explore and understand the value of architecture. Every year for one weekend, private and public buildings open their gates to everyone for free and the city is transformed to a big museum, with its buildings and architecture being the exhibits. Open House in Athens takes place every spring and this year, for the 5th time, during the weekend 31 of March & 1 of April.
More info at http://www.openhouseathens.gr/