Originally built in 1271 under the reign of Kublai Khan, the serene Miaoying Temple (妙应寺白塔, Miàoyīng Sì Báitǎ; 171 Fuchengmennei Dajie, 阜成门内大街171号) slumbers beneath its astonishing high white chorten (also known as a stupa or dagoba), the tallest in China. A glimpse of it rising imperiously above the surrounding hutong is one of the most emotive sights in Beijing. The chorten was built on the site of an earlier temple by a Nepali architect, invited to Dadu (as Beijing was known) by the Khan to cement the new dynasty's relations with Tibet.
You can't enter the chorten itself, but you can circumnabulate the base and explore the temple halls, the largest of which, the Hall of the Great Enlightened One (大觉宝殿, Dàjué Bǎodiàn), contains a display of Buddhist statuary. The Hall of the Seven Buddhas houses scale models presenting the Yuan dynasty cities of Dadu (Beijing), Shangdu ("Xanadu" of Coleridge's famous poem) and Zhongdu, another Yuan-era city between the other two.
The hutong to the north and east of the temple are some of the more atmospheric in the city, and are well worth a stroll after your visit.