Barcelona, Spain

Barcelona, Spain. The back of the card says only "Barcelona: Diverse Aspects." Very descriptive...
But actually, it was pretty easy to Google my way to the answer for all four of these unique buildings.

1. On the left is the Barcelona Cathedral, constructed in the 14th century. It is dedicated to Saint Eulalia, martyred in the city during Roman times. She was supposedly exposed naked in the public square, and a miraculous spring snowfall shielded her from view.
2. Next is the Sagrada Familia, a huge, not-yet-complete, privately funded Catholic church designed by Spanish architect Anton Gaudi.
3. Second from right is another Gaudi masterpiece, the Casa Battló. The local name for this building is "house of bones." The turret-like thing, which looks kind of like the tip of an icing tube to me, may be supposed to be the sword of St. George (patron saint of Catalonia), plunged into the back of the dragon.
4. On the right is yet another Gaudi creation, Casa Milà

Apparently, "works of Anton Gaudi" is a UNESCO site, too!

The stamp is one of a set of three issued in 2010 representing renewable energy. This one shows biomass: organic matter used as fuel.