Lucknow
The Bara Imambara built by Nawab Asaf-ud-Daula in 1784 is an architectural marvel — its central hall is one of the largest arched chambers in the world, built without beams or iron. The Bhulbhulaiya (labyrinth) on the roof is a 489-passage maze where even locals lose their way without a guide.
Hire the official guide at the entrance for the Bhulbhulaiya — going in without one and getting lost is genuinely disorienting.