The Guggenheim museum in Bilbao has an entire wing dedicated to a giant Richard Serra installation that's one with the architectural space it's in. For anyone visiting the Basque country, I cannot recommend visiting the exhibit strongly enough.
And if Spain is too far for some American southerners, there are a couple of Serra pieces in the Chattanooga, TN sculpture park. I was surprised to run into them while I lived there.
Saw it once, it was incredible. I didn’t really know what it was when I first walked into the room and kind of got sucked into it.
This is a simple yet effective description of the unmediated art experience. At the end of the day, art is about standing-in-front-of, and experiencing, THINGS.