Commissioned by Shah Jahan in 1656, this mosque took 5,000 laborers 6 years to complete and is still the largest in Asia, accommodating up to 25,000 worshippers during holy festivals such as Id. Sadly, non-Muslims are not allowed in during prayers, but photographs (sold elsewhere) of the thousands of supplicant worshippers provide some idea of the atmosphere as you wander the huge expanse within. The central pool is for washing hands, face, and feet; to the west (facing Mecca) is the main prayer hall with the traditional mihrab for the prayer leader. You can ascend to the top of the southern minaret to enjoy fantastic views from Old Delhi to the distinctly different rooftops and high-rises of New Delhi — the climb is pretty stiff, but worth it.