Thanks for your comments!
@scorpiuse73 Go for it. It's a great lens for architecture and landscapes. It's well worth having one! On the other hand, it might take a few rolls to get use to it.
@Vick I really like the 12mm. The build quality is superb (better than the 15mm). The lens feels solid and it is very compact. As for the imaging quality, it is not flawless, the corners are kinda soft, it flares rather easily (but I like the way it does), but hey, it's 12mm! If I really need high imaging quality, I use the 17-35mm. But for travelling, the 12mm is perfect! I love it.