The mention of Barcelona above made me realize that I should ask: which style or styles of architecture are you interested in?
Barcelona has lots of great Modernista buildings, some of which you can go inside. Antoni Gaudi is the most famous name, but there are many other worthwhile architects of that style. But, if Modernista doesn't interest you, you may want to go elsewhere.
The mention of Seville reminds me that two of my favorite places in Andalucia were former private homes, where you can see the patios and courtyards - the Palacio de la Condesa de Lebrija in Seville, and the Palacio Museo de Viana in Cordoba. The Mezquita in Cordoba is also something, a mosque with a church built inside it (yes really).
Spain is also substantially cheaper than the places you mentioned in your first post, without being any less worthwhile. Obviously, if you want Nordic design, you won't get it in Spain, but if you are "agnostic" about which styles or periods of architecture and design you see first, consider Spain.
If you like elaborate tilework, you can't beat Portugal. There are patterned tile sidewalks in parts of Lisbon, and great tilework in Porto's São Bento train station. Best of all (worth a trip if you love fancy tilework) is the Church of Marvila in Santarem, an hour outside Lisbon - simply amazing!
Prague has many sgraffito buildings - a layer of white stucco is place over a layer of dark stucco, then some of the top layer is scratched away to make patterns with dark layer beneath. I see from Wikipedia that there are buildings in this style in various places; Prague is where I've seen the largest concentration, and they're quite striking.