From religious perspective, both Islam and Christianity, when a person dies, they remain in the earth and await resurrection for judgment day. Judgment day is the day when God decides to bring the world to an end and awake everyone who has ever walked the surface of the earth to account for all their earth deeds which will be used to decide if they make heaven or hell. So, your answer drawing from religion n will be heaven or hell, that's where we go after death.
However, not everybody is religious or even believe in God to begin with. Hence, it's likely that there are several other theories which some people might believe is the final destination for after life. The Vikings for instance believe in what they call Valhalla, a heaven like place where Gods and men will live forever drinking ales and engaging in regular combat.
Science shouldn't be left out of this topics as it has made believers out of almost everyone through our daily use of science based technologies. Although science is yet to answer the question of life after death with real facts, several unproven scientific theories have been spoken off. The most widely spoke about is the far fetched theory on parallel worlds. Through this theory, It is believed that when we die, our souls begin a new journey of life in a world that is almost like ours, but possibly works in an opposite manner. This theory got it's basis through people who have had N.D.E, near death experience. Theses are people who died for a short period of time but were immediately brought back to life. Almost all of them shared the same experience as they claim to have been in world quiet similar to ours, but different in some other ways. Some said it was like a magical world where they felt no pain and had certain abilities as opposed to life in the real world. People who also woke uo from comas have also claim to have had such emotional and experiences too.
Be I heaven or hell, Valhalla or a parallel universe, no one knows for sure what happens after death. We can only assume through our different faiths, beliefs, and sense of personal reasoning and understand. I guess we all will find out eventually.