What you see in the background of this photograph is the ballot storage area on the second floor. It's enclosed in a cage which requires both a keycard and a fingerprint scan to enter, and only personnel who actually require access to it are granted such access in the first place. Multiple video cameras record what happens in that area 24 hours a day, including video cameras accessible to the public over the internet.
The tour of this facility is self-guided, and you don't need to sign up in advance. Obviously you don't actually mingle with the workers, equipment, or ballots, but the publicly-accessible observation loop completely encircles the facility, and contains information panels along the way to help you understand what you're seeing through the glass.
The photography rule is that you can't photograph anything which could identify a ballot or signature, which is why I didn't take any pictures of the far busier signature verification, ballot review, or adjudication areas.
The other thing you can do after a Washington State election is confirm that your ballot has been received, and that its signature has been verified, simply by entering your first name, last name, and birth date into a form on the state's election web site. I did exactly that after getting home, and found the experience of seeing confirmation that my individual vote actually counted to be surprisingly gratifying.