Dhaka's sights are concentrated in two areas: the old city (Puran Dhaka), where you'll find Lalbagh Fort, the Ahsan Manzil, and most of the atmospheric alleys, mosques, and markets; and the modern city to the north, where Louis Kahn's monumental National Assembly Building is the single most striking piece of architecture in Bangladesh. A half-day walk through the old city and a visit to the Parliament complex are the essentials — give yourself more time to wander if you can.