The Breakers - this is the Rockefeller’s summer home in Newport. It’s open for tours, and though I don’t recall the prices being crazy, it’s definitely been a while.
It’s so ostentatious and over the top, but beautiful, and full of wonderfully made things.
I think it’s interesting to consider our modern billionaire class as equivalents to Rockefeller’s gilded age.
Oh, and while you’re in RI make sure to get a Del’s frozen lemonade.
If you only have one day, and it’s open, I would recommend visiting Rhode Island School of Design’s museum and campus. The RISD museum was surprisingly nice. Small but uncrowded - it was the type of place I could bring a sketch pad and draw for hours. There are probably other museums and attractions nearby, along with nice places to eat and drink. I don’t know much about outside of Providence though.
Rhode Island School of Design is one of the top art schools in the US. They have an art museum on campus that houses pieces like you’d find at actual city museums plus works by their students. https://www.risd.edu/
Theres a killer arcade called Freeplay in Providence. One fee <$10 to get in and all the games are set to free play. Great pinball selection if you're into that. Cheap beer and okish food while you're there. 21+ most days.