Have you tried the Cambridge bus tour? It costs £14 for the hop on/ hop off tour. Take a look online for discounts before booking your tickets. Stops include lots of colleges, the mathematical bridge, the garden centre, American cemetery etc. 

Eltisley

A lovely walk can be found through woodland and the village of Elistey. A great village feel, ornate church and a village green. Great for walking the dogs on an afternoon. 

Harry Potter studios

A nightmare to get to by public transport, but pretty quick by car. It’s not cheap (£29 per adult) but worth it for any Harry Potter fans. You walk through the various sets such as the great hall and Diagon Alley. You also get the chance to taste a butter beer (£2.50) and ride a broom. The photographs and DVDs of you flying a broom are from £12 upwards. You can easily spend 3 hours plus in the studios.