Closer to home, the Manistee County Historical Museum[1], was empty when we visited back in 2003 our our Circle Tour of Lake Michigan. It's a wonderful place, and it was amazing to have the run of it.
During the pandemic on the day we went, we were two of 20 visitors to the Alhambra in Granada, what spectacular luck we had to have a kings view of the place.
I love the prospect of going to the least popular items on this list. The volunteers sound super passionate and not having to fight lines is wonderful.