An exquisite Islamic statement in red sandstone and marble, India's largest mosque was the last monument commissioned by Shah Jahan. Completed in 1656 after six years of work by 5,000 laborers, it's arguably one of the loveliest houses of worship in the world. Three sets of broad steps lead to two-story gateways and a magnificent courtyard with a square ablution tank in the center. The entire space is enclosed by pillared corridors, with domed pavilions in each corner. Thousands gather to pray here, especially on Friday.

With its onion-shape dome and tapering minarets, the mosque is characteristically Moghul, but Shah Jahan added an innovation: the stripes running smartly up and down the marble domes and minarets. The whole structure exudes peace and harmony -- climb the south minaret to see the domes up close, complete with swarms of pigeons, and to see how finely the mosque contrasts with the commercial streets around it. (Women cannot enter the minaret without a man; if you're a woman traveling solo, enlist a man to help you, as the beauty of the architecture is best appreciated from above.) Look into the prayer hall (you can only enter after a ritual purification at the ablution tank) for the pulpit carved from a single slab of marble. In one corner is a room where Shah Jahan installed the marble footprints of the Prophet Mohammed.