Don’t feel you have to tire yourself out visiting college after college. A select few – most obviously Christ Church, with its dramatic Great Hall – genuinely count as tourist attractions in their own right. Otherwise, though, the chief pleasure of visiting an Oxford college is the sense that you’re being allowed a glimpse behind the scenes, into a rarefied world of scholarship and privilege. None lets visitors penetrate all that deeply into its mysteries, though – they’re working institutions, after all – so by the time you’ve seen three or four you’ll probably have seen as much as you’ll ever see.
Schedule a tour or two instead, perhaps one of the Bodleian Library plus a more general walking tour, and then take the time simply to wander the city streets, stroll by the river, and hang out in the central cafes and pubs.