In Cordoba, Espana, I visited the second largest mosque in the world (the first is the Meca). Constructed in the VII century, this is pure history still in existance today and quite possibly the greatest 8 euro investment thus far. We easily spent an entire afternoon impressed by the beauty of this place of worship.
Although originally created as a mosque, it was "transformed" into a Catholic place of worship with the construction of a church in the middle of the mosque (although the Catholics maintained the architecture of the muslems). It was easily one of the most impressive things I've whitnessed as I sat in the pew staring an awe for a good 10 minutes.
Aside from the Mezquita, we were enchanted by the beautiful streets of Cordoba and natural beauty of southern Spain.