The thirty-one planes of existence
Buddhist tradition maps existence as thirty-one floors of reality, each a place where a mind can be reborn.
In Buddhist cosmology, the whole of existence is mapped as thirty-one "planes" or levels of being (Pali ekatiṃsa bhūmi). It is a vertical map of where a being can be reborn — that is, take up a new life after death — ranging from realms of intense suffering at the bottom to refined, blissful, almost formless worlds at the top. Buddhism shares with the wider Indian traditions (such as Hinduism) the idea of rebirth driven by karma (your intentional actions and their long-term moral consequences), so this map is the detailed terrain across which beings wander, life after life.
The thirty-one planes fall into three broad bands. First, the eleven sense-sphere planes (kāma-loka) are worlds where beings, like us, experience through the five senses and crave pleasures; these include the hells, the animal world, hungry ghosts, humans, and several heavens of long-lived gods. Second, the sixteen fine-material planes (rūpa-loka) are subtle heavenly worlds reached by deep meditative absorption, where craving for coarse pleasure has fallen away. Third, the four formless planes (arūpa-loka) are the most rarefied of all — pure states of mind with no bodily form, attained through the most refined meditation. Eleven plus sixteen plus four makes the full thirty-one.
Two points keep this accurate. The map is correlated with states of mind: the meditative calm you cultivate now is said to resemble the worlds you might be reborn into. And crucially, even the highest heaven is not the goal. Gods there live for almost unimaginable spans, but they too eventually die and are reborn elsewhere. Liberation — nirvāṇa, the end of the whole cycle — lies off this map entirely, not at its top. (Nirvāṇa is not annihilation but the "going out" of the fires of craving, a peace beyond the round of rebirth.)