Harlem is uptown Manhattan and  it begins where Central Park ends and extends upt o 155th Street.  Currently (2008) the crime rate is about kin to what it is in Santa Barbara, Calif., i.e. at an all-time low.  Harlem is home to Columbia University, the Cloisters (medieval branch of the Met Museum of Art), the Schomburg Center for Research in Black Culture( writer-poet Langston Hughes ashes are interned here) and the world reknown Apollo where legends were made such as Ella Fitzgerald, Cab Calloway, James Brown and Michael Jackson. Harlem is also home to three of New York City's finest row house neighborhoods. The three neighborhoods are Mount Morris Park, Central Harlem & Hamilton Heights and they all have landmarks status because of their fine architectural work. The streets are much less crowded than midtown but you will always find thongs of people on 125th street working, shopping or just enjoying the sites.  Subway trains  #2 or #3 takes you right up Malcolm X Blvd. (formerly/also known as Lenox Ave.; remember the "x" and you'll remember this is the same street).  You can get off at 116th to visit Harlem Heritage tours  (call ahead for soul food, basketball, music, history tours) or eat at the fabulous Amy Ruth's, stroll through the historic Mount Morris preservation area. You can also take the A train ( Ellington's A train) to 125th Street &  visit Welcome to Harlem Tours which is right around the corner on 8th Ave./Frederick  Douglass Boulevard. They too offer many tours but you must call in advance.  The locals are accustomed to tourists in the "tourist-y" areas (more southern parts of Harlem), i.e. 125th street, Harlem's main drag where one can see the Apollo Theater (or perhaps even attend the famous Wednesday night amateur night, book tickets online), president Bill Clinton's new office building, eat at Sylvia's soul food (on Lenox/Malcolm X just above 125th), etc.

There is also East Harlem, predominantly Latino culture and food.

Harlem is very big and hard to cover on your own so visitors may find it easier to take a tour, either a hop on hop off bus tour (I think it's Grey Line), a gospel or soul food/jazz tour (Harlem Spirituals does a few and their buses depart from midtown), walking tours  ( Welcome to Harlem & Harlem Heritage Tours).  Harlem Heritage Tours can also take you to basketball games.

Note about taxis:  historically Harlem has had their own taxi system as many years ago the yellow cabs wouldn't go up there.  Nowadays the crime rate is WAY down and downtown yellow cabs will definitely take you up there, it just might be difficult to flag one down on your return trip home if you feel like grabbing one.  Why?  They are competing with the more glamorous Harlem cabs.  Just look for the finest cars on the streets (i.e. Lincoln towncars, etc.), stick your arm out and wave, get a quote for your destination (there will be a license in the window but probably not a meter) and away you go, cruising along in the finest ride you'll get in Manhattan.

 Harlem hotels and b&b's are much cheaper than lower down in Manhattan; there is also a Harlem YMCA.