The Citadel is a separate walled compound inside the larger old city, ringed by its own wall and moat. Most of the original royal buildings are in ruins, but several survive in a recognisable form. The Gagan Mahal, where the sultans gave public audience, has two massive arches still standing. The Sat Manzil ("seven storeys") is the truncated remains of the palace tower; the upper levels are gone but you can climb what is left for a view across the citadel. The Jal Mandir, a small pavilion in a stone tank, was the sultans' summer pleasure house.
Allow about an hour. The walking distances inside the citadel are larger than they look on the map; there is little shade and few signs.