The Temple of Heaven is the chief Taoist temple complex, built around 1420 and thereafter visited every year by the emperor until the revolution. It's built on very expansive grounds that are in serious need of a makeover. The earth is parched and only patchilly covered with grass, which is ironic because the sole purpose of the temple was to pray for rain. There are all sorts of numerical tricks involved in the construction which are meant to represent certain numerical facts about the universe. To the layman, however, the main point is the large multi-tiered altar representing various levels of the universe. On top of that is the Hall for the Prayer for Good Harvests, which is an impressive building used only by the emperor once a year. There were all sorts of complicated rituals surrounding the rain prayers, and any slight mistake or bad omen would presage a disastrous growing season, so this was taken very seriously. The interior is dazzlingly colorful and airy as well.