Truman's Little White House in Key West is pretty fascinating. The guy that gave us the tour is one of the best guides I've ever seen.
Not a museum, but one time back when I was working in college athletics, I went to one of our away basketball games over winter break because the opponent needed help staffing the game with all the students and majority of the staff gone. Rode on the bus with the team, so got there way earlier than I needed to be, but I didn't want to do the 6-hour round trip drive to save an hour.
So I decided to walk around campus checking out the athletic facilities or any other building on campus that was open, which wasn't much since nearly everyone was gone. Even though I don't like baseball much, it was at the top of my priority list because it was new and pretty lavish for the level they play at.
One of the baseball coaches was in the office, which was at the baseball facility.. He saw us, came out to greet us, and gave us a tour of the facility inside and out - showed us the coaches offices, locker room, training room, indoor batting cages, etc. Basically got to see everything that would normally be off limits to regular ole joes like myself.
Was pretty neat, he gave us all the inside info on how it came to be and everything. The real story, not the fancy PR version the school would give you. Turns out their financing campaign was pretty easy. They had an alumnus that was a pretty significant MLBer back in the 90s and 2000s, 7x All-Star, made nearly $100 million for their career, etc. They called him up and asked if he could donate some money towards the cost. He just asked them how much they needed to fully fund it and he sent in a check for that amount. One call and the fundraising campaign was done lol