While the Alhambra has been around for more than half a millenium, the Sagrada Familia will not be finished for decades. But it is still one of the most stunning things I have ever seen. Normally a great building reminds you of others of the type you have seen, be it a Mughal palace, a Hindu temple or a Gothic cathedral. The Sagrada is like nothing I have ever seen before, and I can't say how much that impressed me.
Gaudi was inspired by nature, so the Sagrada is all about curves and organic forms. It looks like it has grown out of a coral reef, or leaf litter. There are snail and lizards for gargoyles, pillars like tree trunks, steepletops like flowers. Go and see it.
A stairwell in one of the Sagrada's towers.