It's 17.50 - general admission and 13.50 for senior(65+), students (11+), and active US military. I went on a Tuesday, and as it is off on tuesdays they gave a 2$ discount card to use next time.
It is not free. We purchased a Groupon for it.
It is free for Google employees, but $17.50 adult admission
There is a discount for late in the day. I believe I paid $10 two hours before closing.
It's definitely not free...
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