India, Jan. 4 -- The majestic Humayun's Tomb was blanketed by a thick layer of fog, as a group of history enthusiasts, packed in layers of clothing to fight off the morning cold, huddled around to learn more about various structures within the vast complex.

Saturday marked the third heritage walk in a series that the Municipal Corporation of Delhi (MCD) is conducting. Sanjeev Kumar Singh, an executive engineer with the MCD heritage cell, kicked off the day's history lessons at 9am with a discussion on Humayun's Tomb, built in 1565-72 AD, which houses more than 150 graves in 60 chambers.

According to the Archaeological Survey of India, Humayun's grieving widow Hamida Banu Begum had built the mausoleum. The tomb itself is made mostly of q...