A railway turntable is used to redirect or turn certain rail vehicles from one track to another when space is too limited to install a switching system.
The turntable consists of a rotatable steel bridge structure set into a circular, recessed pit. The bridge of the turntable is supported at both ends by wheels that roll along a circular rail anchored to a reinforced concrete beam inside the pit.The tracks connect radially to the turntable.

This is what the locomotive sees while turning.