Check out the Morgan Library & Museum - Madison and 36th. Great architecture.
The Morgan Library & Museum, New York, founded by Pierpont Morgan
Another little but very impressive gem are Faberge eggs at the Met:
https://www.metmuseum.org/exhibitions/listings/2011/faberge
I would also prefer that everyone stop acknowledging BXL. That's a hidden gem. All locations. So is The Ginger Man on 36th.