#Wikipedia documents in many languages the buildings that are of such a significance that they are officially recognised as "monuments". All these articles need illustrations and Wiki loves Monuments is the photo competition that rallied people from all over Europe to take pictures of the buildings and its details.
Once all this pictures were in, Europeana selected some to create its first user generated exhibition online called: Wiki loves Art Nouveau. The exhibitions shows of European Art Nouveau in four themes: exteriors, interiors, details and author's pick.
If you do not know Europeana yet, visit their website. They are the portal that brings more and more of the European cultural to the Internet. They are also instrumental in gently pushing European GLAM towards using free licenses.