The correct answer is option 3, Qutub Minar. The Qutub Minar is a UNESCO World Heritage Site located in Delhi, India. The Alai Darwaza Gate is one of the entry gates to the Qutub Minar complex. It was built by Alauddin Khilji, a ruler of the Delhi Sultanate, in the 14th century. The gate is made of red sandstone and exhibits beautiful intricate carvings and designs. It is a significant example of Indo-Islamic architecture and adds to the overall grandeur of the Qutub Minar complex, which also includes other historical structures such as the Qutub Minar itself, the Quwwat-ul-Islam Mosque, and the Iron Pillar of Delhi.