In Aztec (and other ancient Mesoamerican) mythology, after a person dies, their soul journeys either up the twelve steps toward lightness, or down the nine steps into darkness. After passing through these steps, the soul enters one of three afterlives: Tonatiuhican, the House of the Sun, for those who achieved the highest spiritual goals in life; Tlillan-Tlapallan, the Land of the Fleshless, for those who have successfully applied the teachings of Quetzalcoatl and learned to live without physical incarnation; and Tlalocan, the Land of Water and Mist, for all the other basically good-hearted simple people. Bad people go to Mictlán, a dark, boring place.
Of course, the evidence is open to interpretation; some sources say that Tlalocan is the afterlife only for those killed by lightning, dropsy, and skin diseases and those sacrificed to Tlaloc.
Tlalocan is a simple, materialistic, pastoral paradise. Souls play leapfrog, catch butterflies, sing, and take delight in their senses. The land is lush and abundant with flowers, corn, and all growing things. Everyone is happy and giddy and lighthearted and frolics all the time.
After four years of this paradise, the soul is reborn on Earth, and the cycle goes on, unless in some future life the soul should devote itself to loftier or baser pursuits, destining itself for one of the other afterlives. For most souls, this will never happen.
Tlalocan, as its name suggests, is ruled over by Tlaloc, the god of rain, and in some cultures also a god of war. Since all his subjects are completely happy, Tlaloc doesn't have much to do in a ruling capacity but to let water flow from his fingers into the beautiful babbling brooks and occasionally give orders to his Tlaloques, mini-gods who act as go-betweens from this place of rebirth to the physical world and back. Not to fear, he still has plenty of time to foster war among his people on Earth and claim sacrifices.
The most famous representation of Tlalocan is a wall fresco uncovered in Tepantitla, a district of Teotihuacan. More recent evidence suggests, however, that this painting may in fact represent the Teotihuacano Great Goddess and the beginning of civilization rather than Tlaloc presiding over Tlalocan.