Why is it difficult for visitors to locate Cambridge University?

"Where is the university?" is a question many visitors to Cambridge ask, but no one could point them in any one direction because there is no campus. (14) The university consists of thirty one self-governing colleges. It has lecture halls, libraries, laboratories, museums and offices throughout the city.
    Individual colleges choose their own students, who have to meet the minimum entrance requirements set by the university. Undergraduates usually live and study in their colleges, where they are taught in very small groups. Lectures, and laboratory and practical work are organized by the university and held in university buildings.
    The university has a huge number of buildings for teaching and research. (16) It has more than sixty specialist subject libraries, as well as the University Library, which, as a copyright library, is entitled to a copy of every book published in Britain.
    Examinations are set and degrees are awarded by the university. (17) It allowed women to take the university exams in 1881, but it was not until 1948 that they were awarded degrees.