On a budget, Cambridge (day-trip) still earns its price.
~£25–£45 rail + punting ~£20
Punting past the Backs with the great college chapels rising behind is one of England's loveliest set-pieces, and the town is walkable and atmospheric. The honest catch: it's a full day with train cost and travel time, many colleges charge or restrict entry, and in peak season the river is a punt traffic jam.