Ok the restaurant in the space needle is not open. Sandwiches and drinks can be purchased but the price is outrageous if you care.
Not sure about the Space Needle itself, but The Armory food court next to the Needle has lots of food options. There's also the Collections Cafe at the Chihuly exhibit.
It looked like there were a couple of coffee stand/small cafes, but not a restaurant. The restaurant at the top is gone, not sure if it is going to reopen.
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