Go for lunch at The Wrestlers on Newmarket Road. It looks pretty dire from the outside, but the food (if you like Thai) is heavenly. You'll also rub shoulders with about 85% of the Cambridge software industry in there. When you're not there, also visit Clowns, on Kings street - a lovely little Italian cafe. The best coffee in Cambridge, and the gnocchi pomodoro is perfect. Oh, and spend a couple of pounds to go up the tower of St. Mary's church, which gives you great views across the city. When you're bored with that, travel up the road to Ely and have a look around the cathedral, and drink a nice cup of tea at Poppies, by the river.