Less than an hour for sure
Not more than half an hour
As long as you wish. Not a lot to see in the Castle.
About a half hour to 45 minutes.
It can take as like as 10 mins.
The architecture is cool so go through it all. Nice collection of historical pieces that are missed by most that just see the cafe etc which doesn't have good food and is pricey. They have a to scale model of national mall which is a hit with all. Small compared to the museums but definitely worth a visit.
Not really much to see. It is like an administrative building for the Smithsonian institution
There is not a ton to see in the castle. There is a great café and gift shop. There's a couple of maps of the Smithsonians and a little bit of history. There are also amazing gardens which can take significantly longer than the inside if you are a gardener.
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