Once you're at the uni (hoping you do come to Durham!) you'll see that walking from town to the hill colleges really isn't that far at all! Particularly if you have to go further than the science site for your lectures!
(Of course, if you do just spend your entire time walking that tiny path from Grey to the science site and no further, town will probably start to seem like a massive hike on the odd occassion that you want to go shopping!)
Anyway, hope you enjoyed the open day.