Given Cambridge's location on the main eastcoast rail line and its proximity to London Stansted Airport you can travel to the rest of the United Kingdom and Europe easily and cheaply. While it's tempting to spend as much time as possible traveling during the semester, it's important to balance the amount of time you travel with the amount of time you spend experiencing Cambridge and the surrounding area. If you get involved with student activities and/or are keen to experience Cambridge and the UK during the semester, you might want to consider arriving in Europe before your semester or staying after to do the bulk of your traveling then.
Cambridge is only about 50 miles north of London and there is a frequent train service between Cambridge and London's King Cross and Liverpool Street Stations. Cambridge students should consider purchasing a 16-25 Railcard upon arrival into the United Kingdom to received 1/3 off all train tickets purchased for a year. This makes dinner and a show in London a cheap option for Cambridge students.
The links to follow have been found useful by past students when planning travel. While these are not endorsements for any particular travel companies, they represent the possibilites for travel from Cambridge.
Visiting London London
Travel in the UK
Travel in Europe