Best of luck with your visit to Karachi here is a small list of what Karachi can offer!
Major attractions;
*Mazar-e-Quaid - tomb of Muhammad Ali Jinnah, founder of Pakistan
*Mohatta Palace and museum
*Karachi Port Authority's Water Jet fountain
*Masjid e Tooba - largest single-domed mosque in the world
Beaches and Waterfront;
*Clifton Beach
*Kemari jetty (for boat ride, fishing, and live sea food)
*Beach Park
*Jehangir Kothari Parade
*Hawke's Bay Beach - breeding ground for endangered turtles
*Paradise Point - rock promontory in the sea with a natural arch
*Sandspit Beach
*French Beach
*Mubarak Village
*Sonehra Village
Museums;
*Pakistan Air Force Museum
*Karachi Expo Center
*PIA Planetarium
*Pakistan Maritime Museum
*National Museum of Pakistan
Colonial Buildings;
*Merewether Tower (of the freemasons)
*Frere Hall
*Saint Patrick's Cathedral, Karachi
*Sindh High Court
*Empress Market
Islands;
*Clifton Oyster Rocks
*Bhit Shah Island
*Buddo Island
*Bundal Island
*Churma Island
*Manora Island
Amusement Parks;
*Arena
*Go Aish Adventure Park
*Dream World
*Safari Park (University Road)
*Aladdin Park (Rashid Minhas Road)
*Sindbad
*PIA Planetarium
*Karachi Zoological Gardens (Gandhi Garden)
*Cosy Water Park (super highway)
*Samzu Park (super highway)
*Fiesta park (super highway)
*Sun Way Lagon (near Nooriabad)
*Polo Ground (PIDC)
*Cheekoo water park (super highway)
City Parks;
*Bin Qasim Park (Old Clifton)
*Beach Park (Sea View)
*Askari Park (University Road)
*Hill Park (Tariq Road)
*Nisar Shaheed Park (Defence P5)
*Zam Zam Park (Zamzama)
Famous Avenues;
*Zamzama Avenue (famous for its designer outlets & restaurants)
*Beach Avenue
*Karsaz Road
*II Chundrigar Road (Karachi's Wall Street, the great Habib Bank Plaza and the MCB Tower)
*Shahrah-e-Faisal
*Tariq Road (Shopping street)
*Sunday Bazar in DHA (for cheap bargain shopping of used and new items)
Food;
Burns Road
Highway
DHA Phase VIII
Boat Basin
*Note that I have mostly copied the list from another site that I know of, I have not compiled all the list my self.