London is 50 minutes on the train to Kings Cross. The station is out of the centre, but a 20-minute walk can get you there. Alternatively, buses stop there regularly (tickets cost £17 return with tube all day).
Ely is a small town outside of Cambridge famous for its cathedral (started 1081). It also has Oliver Cromwell’s house on St Mary's street.
Duxford has the best aircraft museum in the area. Buses leave from Downing Street in Cambridge at 10:25am and 12:25pm, and are free. The autumn air show is on October 13th.
Anglesy Abbey is part of the National Trust, started in 1600, and has paintings inside as well as really nice gardens.