I'll say Rome, just because.
Wrong! and I'll murmur why later.
On architecture, I just like it, am no architectural historian. I have friends who are, and they are way more into details of it than I am. I just like spaces, which are formed by walls or groves of trees or bodies of water, or distribution of decks of cards, as the case may be. Took me years to figure out that this interests me..
ohmygoodness! I just googled this!:

It says: San Carlo. Is that in Rome?
That's the SAME pic and I'm STILL not sure! I think my sister went there on her honeymoon!
Sorry, having slowness difficulties with a2k.
It's Rome and I'll tell you why, from my point of view.
Look at those beefy columns holding up the elaborate ceiling...
look at the love of curves.
look at the symmetry...
that's baroque, and Rome od'd on baroque.
Borromini was a master of it, and his works are all over Rome, including Sant'Ivo's and much else. His pupil Bernini gives him a run for his money and I don't know which I like better, I love both of them, or their works.
Nothin' this Over the Top in Tuscany, that I know of.
Milan, well, the cathedral is over the top, but in a different way.
Woohoo! Beautiful.
NOW I know where I've seen it. My sis has a pic very much like that one. I'll be back in a few.
Well, that's why, plus I've been there a few times.
If you ever get to Rome, again from my pov, I'd pass on St. Peter's - well, no, but I wouldn't spend all my time there and in the vatican. First I'd get gelato and walk.
The photo is the dome of San Carlo alle (at) Quattro Fontane, meaning at the intersection of two streets, with four fountains at the intersection. That church, photo to follow, is by Borromini. Just a bit to the west is Sant'Andrea del Quirinale (the presidential palace is across the street, called the Quirnale), and Sant'Andrea is by Bernini, pupil and rival.
Both of these are jewel boxes.
Good eye, osso. You really seem to have a love for it despite your modesty. If I ever get there, I'll definitely call on you for pointers!
Okay, where is THIS?:
The facade seems jumbly to our eyes, but the interior cloister is a cool and strong, elegant, space. No link.
Beautiful. I am just fascinated by 'old' architecture.
It's soooo familiar and I've no idea. Very foursquare and stalwart...
Okay, here's a very vague hint for now -
It's not where you think it might be!
Hah, I was thinking New York or Boston.
Wild guess, St. Patrick's Cathedral?