Nearly all trace has indeed gone after centuries of intensive occupation but they were once modest hills, usually remaining dry when the river flooded (see 1201). They lie between the two branches of the River Granta which have shaped central Cambridge (see Roman Cambridge).
One branch formed a now-long-gone river valley running through Pembroke Leys (now the Lensfield Road & Newtown area) and possibly the forerunner of the King's Ditch from about modern Pembroke Street to Quayside.
By way of example, have a look at St Benet's churchyard from the junction of Benet St. and Free School Lane: note how much the occupation level has risen in the bustling streets compared with the medieval churchyard. This picture is from the other side, looking towards that corner.
Hills Road refers to the Gog Magog hills, both being on the route of the Via Devana.
There's also an article on this in the Cambridge Cycling Campaign's Newsletter 22: The Hills of Cambridge