The Qutub Minar complex in South Delhi is one of the most impressive architectural sites in India. The minaret itself — 73 metres of intricately carved red sandstone and marble, built in stages from 1193 — was the tallest brick minaret in the world when completed and remains extraordinary. You can no longer climb it (it was closed after a crush in the 1980s), but seen from the ground it is still overwhelming.
The surrounding complex is a dense layering of history. The Quwwat-ul-Islam mosque — "the might of Islam" — was the first mosque built in India after the Islamic conquest, constructed using columns taken from demolished Hindu and Jain temples. The columns are still there, clearly non-Islamic in style, incorporated into the new design. The Iron Pillar, also in the courtyard, was brought here from elsewhere and predates the mosque by nearly a millennium. The Alai Darwaza gateway (1311) is a masterpiece of early Delhi Sultanate architecture. Allow two to three hours.