Our school only has a little over 1000 people and everything is in walking distance unless you want a ride into town/neighboring school about 10 minutes away. That's what pledges are for, though.
Yeah, our campus is in the middle of the city it's in. There are 26,000 undergraduates and I think the city is something like 100,000 people. There's a bar on campus and a bunch of fraternity houses around stuff near campus, but a lot of people go off campus to party and drink, I think (I wouldn't know first hand
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I'm not sure what the percentage is, but I'd guess that only ~10% of the people in my college (not university, college -- the college of natural sciences) are involved with "Greek Life."