FYI you can just go to any lecture, noone's going to ask you if you're a student, or kick you out if it's not in that list. Here's a list that has Wharton lecture meeting times - https://syllabi.wharton.upenn.edu/index.cfm
. You can probably find the same for Engineering, etc. -- or just ask a current student to get the info from Penn InTouch. (If you're only going on a weekend then this information is useless, but checking out classes would be cool if you do get the chance at some point.)
Also Penn Park isn't really impressive enough to take time out of a campus visit to see it.
Definitely just walk around all the major buildings and College Houses - get inside as many as you can. The libraries are really nice - do check out Fisher if you can! Van Pelt is pretty nice too. Meet people if possible - just approach someone that looks like a student on Locust Walk if you want and ask them questions. Ask about favourite classes, best study places, favourite restaurants, etc.