Garden of Eden
I was then said to be sealed off after Adam and Eve's exile, and gaurded by the spinning blade of a sword. (An object that was not yet invented.) And also by angels in order to prevent the humans from returning.
It's believed to have been located in Mesopotamia based on the scripture at Genesis 2:10-14 which says: "10 Now there was a river issuing out of E′den to water the garden, and from there it began to be parted and it became, as it were, four heads. 11 The first one’s name is Pi′shon; it is the one encircling the entire land of Hav′i‧lah, where there is gold. 12__irrelevant__13 And the name of the second river is Gi′hon; it is the one encircling the entire land of Cush. 14 And the name of the third river is Hid′de‧kel; it is the one going to the east of As‧syr′i‧a. And the fourth river is the Eu‧phra′tes."
Interestingly, if these rivers really did run through the garden, then it would tend to conflict with the concept of the Great Flood which would most likely have changed the geography to a point that these rivers would be unrecognizable at best.