Assuming a car:
Upper Treman State Park, Taughannock Falls, Cornell Dairy Bar, Cornell Plantations, Ithaca Farmer’s Market on weekends. From there you can take a boat ride on Cayuga Lake. If they’re doing that then.
There’s lots of restaurants, best thing maybe is to look them up on Yelp or something.
If you want to eat like a Cornellian who should be studying (of my era anyway) you can get a Sui or an MBC at the Hot Truck in back of West campus.If you can figure out when it’s open. Or, more easily, at Shortstop Deli downtown.
Check Cornell and Ithaca websites & newspapers for things going on around the area while you’ll be there.
You could also see if any of the links still work from this old post:
.http://talk.collegeconfidential.com/cornell-university/1638407-whats-happening.html
Probably most of them are obsolete, but I’m far too lazy to re-do it.