Incoming senior - how to make the most of my last year at KU?

This will be my last year at KU and I really want to make the most of it because I love this place. I haven't been the most involved in my college career, because of introversion/long term relationship/etc.

I want to join a club or organization like the rock climbing club but I'm not sure where to start. Other than that, how should I take advantage of being here for one last year?