The neighborhood to the north and east of Morningside Heights.
Widely perceived to be an unsafe part of New York City.
You can go shopping on 125th Street, which is only a few blocks away, but most Columbia students prefer to waste hours on the subway to get somewhere with the same collection of stores. Go figure.
Once, Harlem had a Renaissance, and was a mecca for African-American artists, musicians, and writers, like Langston Hughes. Then half the neighborhood was demolished to make way for projects, the city disinvested in services when whites fled to the suburbs, and lots of people got addicted to crack. Now, the term "Harlem Renaissance" is used to describe the repopulation of Harlem by upper middle class yuppies priced out of the rest of Manhattan.