For me it is hands down THE EXPLORATORIUM on Lyon Street in San Francisco. "The Museum of Science, Art and Human Perception". Ever had the good fortune to visit it?
It's a wonderland of exhibits. Teachers bring their classes there to "play" and learn. There are hands-on exhibits you try on for size. There are lectures going on covering all kinds of nifty things. It's set up so that any person of any age will be informed mystified excited enthralled.
I have never been to the Smithsonian. I expect that would top the list for everyone. A zillion buildings and tons of historical things pertaining to my country t'is of me and mine and thine. Surely there are other magnificent museums...some specialized, some generic....all over the world. That would be a fun thing for a wealthy person to do. Visit the museums of the world and soak up the information and history.
An interesting bit of trivia ... Joseph Strauss, the engineer of the Golden Gate Bridge, designed the Longview-Rainier bridge.
It was originally a privately-owned toll bridge, and was (in 1930) the longest and highest cantilever bridge in the US.
https://en.wikipedia.org/wiki/Lewis_and_Clark_Bridge_(Columbia_River)