Chandi Chowk is undoubtedly one of the busiest markets in Delhi. And also one of the oldest. It was designed by Jahan Ara and built by her father Shah Jahan - the great emperor of India.
It is a place were you can buy all sorts of spices, nuts, vegetables, fruits and probably many more. The traffic is insane, so it is better to find a good riksha man, who will take you around. The air is filled with spices smells. There are things to be seen and bought there, which I cannot even name or place. It is better to see :)