Where did Clay first see Hannah?

Clay first saw Hannah at Kat's going away party.

You pushed him off and stood up. Then he stood up, and you both looked at each other, not sure of what to do. And your decision? You ran back down the street while Kat and I laughed like crazy in the window. I remember that. Kat thought it was so funny. She told me about it at her going-away party that summer.

The party where I first saw Hannah Baker.