Are there any? Preferably lots of classical architecture all over the place, in the ships, on the ships, on planets, in planets, in space... Pillars, ornaments, decorated vases, flowers, gilded curved chairs, all the extravagance and grandeur befitting a post-scarcity society. Bonus if people's clothes are inspired by classicism, with lots of unique patterns and colour. Looking for examples. Will have lots of this in my own work and want to see how other authors handled it.
I don't know any sci fi novels that do this specific thing, but when I looked I found this https://www.oobject.com/category/15-scifi-movies-15-famous-architectural-locations/ . I know it's not quite what you're asking, but maybe these films can inspire you? But there's also 'The ship who searched' (Anne McCaffrey und Mercedes Lackey), whose protagonist is a brain encased in a starship. She has interest in archaeology, and there's a chapter where her human partner discovers ancient tombs filled with treasure.
Gene Wolfe’s Book of the New Sun. I don’t recall Frank Herbert saying much about the architecture but it wouldn’t be out of place in Dune.
Dune had castles and whatnot. The Japanese novels Legend of the Galactic Heroes had classical architecture all over the place, on the ground and in ships.
Now that I think about it... general fiction, but Wilbur Smith's 'The Sunbird' is about an archeologist who discovers an ancient city in Botswana. Lots of treasure and description in there.
I've heard of it so much, yet it completely passed my mind. But it might be hard for me to go through one of those books, I just find the whole 40k universe so alien and absurd. Should give it a try though, may be pleasantly surprised. Thanks. Edit: I mean the humans feel alien, they feel mechanical in nature.
It's got to be prevalent in the subgenre of alternate timeline stories (which is what the New Sun series MIGHT be, or is it set in the future? ) Also check Wolfe's 5 Heads of Cerberus, consisting of 3 novellas, one set in an old French style colony similar to New Orleans, all based on 18th century French architecture. Alternate timeline stories tend to be set in the well-known historical periods, just with one crucial difference, like the Nazis won WWII or whatever. I'm not sure they should really be classed as sci-fi, but with the limited categorization offered by bookstores, that's where it goes. It should probably just be considered speculative fiction.