This is the dargah or shrine of a Central Asian mystic by the name of Qutubuddin Bakhtiyar Kaki, who was the disciple and successor of Moinuddin Chishti of Ajmer. Bakhtiyar Kaki was a prominent Sufi saint who spread the message of love in pre-Mughal Delhi, and his shrine in Mehrauli is revered by thousands to this day. The area is a royal necropolis today, since many later royals chose to be buried near the saint. The marble domes on the left are part of the Moti Masjid, built by later Mughal king Bahadur Shah I.
It is believed that the Qutb Minar was named after this saint of Mehrauli.
Thanks to Shalabh for this lovely photograph!
To learn more about this series and see more pictures of this incredible city, check out this link.