In Indiana Jones and the Kingdom of the Crystal Skull, a short while before the ending of the movie, there was a long trail in the temple and eventually Mac and Spalko died inside the temple. Then, the temple crumbles, and a flying saucer rises from the ground and disappears as then the Amazon river floods the valley. Then Indy asked, "where did the alien go?" to Oxley, he replied, "Into the space between spaces.".
Indy : Where did they go? Space?
Oxley : Not into space. Into the space between spaces.
Which space Oxley mentioned in the movie as space between spaces?