Charminar, a Mosque of the Four Minarets, was built in 1591 by Sultan Muhammad Quli Qutub Shah, shortly after he had moved his capital from Golconda to Hyderabad. Apparently, he vowed to built a masjid (mosque) if a plague that was ravaging his city was eliminated.
Charminar lies in the center of Old Town and is surrounded by several markets with thousands of shops each. The most famous one of them is called Laad Baazar. I dedicated a separate post to it.
For a small fee (foreigners - 100 rupees/2$; Indians - 10 rupees) one can enter the masjid and through the winding steps in one of its minarets reach the top floor, from where there are great views of the surrounding Old City.
Charminar and its four minarets:
A hospital and one of the street markets: