The place, referred to in Genesis as a garden, where human history began during the Week of Creation. God made Adam and placed him in Eden. God then created Eve there, so that she and Adam could complement and accompany each other.
From these two parents, the entire human race is descended. After the rebellion of Adam and Eve, they were evicted from Eden. During the Great Flood in 2304 BC, Eden was destroyed along with all the other geographic features of the antediluvian world.
A good argument could be made that the ruins of Eden lie buried deep in the Earth's crust beneath the modern city of Jerusalem, but in fact no person alive today knows for sure.
After Adam and Eve were kicked out of Eden, its gates were guarded by an angel with a fiery sword.