Just outside of Madrid, Museo del Aire is actually a pretty good air museum. It is free (but accepts donations), so it does not have a lot of funds, and some of the signs were damaged by weather and waiting replacement. Nonetheless, what they had is worth the trip if you're interested in planes. Minus side is the opening hours that are quite limited: only 10:00 to 14:00.
Half the collection is outdoors and the other half inside hangars:
Multiple hangars with more aircraft:
Nice collection of engines:
The last (or actually first) hangar had world war 1 planes:
I also have to give them credit for recognizing the French inventor, Clement Ader, who made the first heavier than air flying machine (using a heavy steam engine), 6 years before the wright brothers. Sadly that machine didn't work well but it still flew:
The museum was definitely worth at least 2H if you care about flying things :)