<p>I would suggest Commons, unless you meet a student who would take you to one of the colleges. It’s pretty impressive, and freshmen generally eat there pretty often. You also don’t have to gain entrance to a residential college courtyard to go there, and you can check out the Woolsey Hall rotunda, and maybe the Beinecke library while you are there.
I think you can just walk in and pay cash, but I’m not sure of that.</p>