the best thing to explore is the backs also I would say going to the mill (14 Mill Lane, Cambridge, CB2 1RX) for a quick beer in the summer is a must you can also get a punt but beware the punt guides they are a rip off unless you are a wimp and dont want to punt yourself !
the market is nice on a good day but like so much of cambridge it depends on the weather
if you like book shops your in for a treat there are plenty around stay away from borders and do everyone a favor and dont give them your money try the second hand and speciality shops such as G.David. Bookseller. Est. 1896 which is on 16 St.Edwards Passage, Cambridge, CB2 3PJ
or the legend that is Brian Jordan Music, Books and Facsimiles (if your into classics then your lucky)