South Dakota Air and Space Museum
Ellsworth AFB, South Dakota
"South Dakota's official warbird sanctuary." Military aircraft and rockets from World War II to the near-present day are on display here. Because of their size, most are exhibited outdoors. There's General Eisenhower's WWII B-25, a B-52 Stratofortress nuclear bomber with its Vietnam War camouflage, a Titan I ICBM, a supersonic B-1B, and Nike Ajax and Minuteman missiles as well. Historical military aviation fans can geek out viewing a restored B-29, a C-47, an A-26, and an F-111A Aardvark.
Another advantage of having these sometimes-giant aircraft displayed outside is that you can hang out under their massive wings if there's a downpour or if the prairie sun gets too hot. You won't be bothering anyone at this little-known museum. You may well be the only visitor.