Cambridge is readily accessible from various locations.
From London terminals. Trains from London terminals (Kings Cross, Liverpool Street) are quite frequent. Please, see http://www.nationalrail.co.uk/ for train times and ticket bookings.
From Stansted Airport. The nearest airport is Stansted, and direct trains from Stansted Airport to Cambridge leave hourly (journey time about 30 minutes). Direct coaches from Stansted Airport to Cambridge city center (Parkside) are also available and may be the only option for late arrivals (journey time about 50 minutes): please, see http://www.nationalexpress.com/ for coach times and ticket bookings.
From Luton Airport. Direct coaches from Luton Airport to Cambridge city center (Parkside) are available (journey time about 1.35h). http://www.nationalexpress.com/
From Heathrow. Underground (Piccadilly line) to King's Cross (journey time about 1 hour) and train King's Cross-Cambridge (journey time about 50 min by fast trains: 14 and 44 past the hour).
Newnham College is 30 minutes from Cambridge rail station at a brisk walk (map). We recommend that you take a taxi from the station to Newnham College Porters' Lodge, which costs £6-£7.