Boston Avenue Methodist Church in Tulsa Oklahoma. One of the few examples of Art Deco religious architecture in the world. It’s unique and quite impressive to see in person. I don’t know if they still do but they used to offer tours of the building on Sunday afternoons.
The Philbrook is great, and there are a couple smaller, local galleries that are really great too.
The Gilcrease, Aha, Woody Guthrie Center, Sherwin Miller, Greenwood Rising, and the Discovery Lab are solid.
Lovetts and MA Doran are great showcases.