A secluded stretch of sand about 40 km west of Karachi along the Makran Coastal Highway. French Beach is one of the few clean, swimmable beaches near the city, with clear water and rocky coves. The beach is privately managed, so you'll pay a small entry fee, but that keeps it less crowded than Hawke's Bay or Sandspit.
Locals run small operations serving freshly caught fish, lobster, and prawns cooked on the spot. Snorkeling is decent close to the rocks. During the monsoon months (roughly June to September), waves pick up enough for surfing, though you'll want to bring your own board. Basic huts are available for overnight stays.
The drive out from Karachi takes about an hour and passes several other beaches along the coast. It's a popular weekend escape for Karachiites.