+1 for citypass
I went after 6 and it was only $19- I still had plenty of time to explore and see everything. The only thing that I didn't get to see was the live glass blowing they do, I think it usually ends around 4ish..
It is about $25 per adult. If you buy it with a ticket to the space needle it is cheaper
About $25
26 and 13 for kids If You.buy all kids tickets they work because they don't pay attention to the tickets
Groupon usually has deals
It's $29 for general admission per person but I suggest you get the Seatle City Pass, it is worth it if you want to do multiple attractions!
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