The opposite of heaven, hell is traditionally a place where wicked or evil people go in spirit form after death. Depending again on your belief system, hell can be a fiery pit of eternal damnation, as it is for the Christian and Islamic traditions, or a grey underworld as it was for the ancient Greeks, or eternal fire as it is in Jewish traditions. Jean-Paul Sartre felt that hell was other people, while some think hell exists within us all when negative thinking gets the upper hand.