On the tube how do the trains turn around when it's the last stop?

Update: London underground: like they can't go back on the same line so how do they turn round, or get to the otherside?
Update 2: I know that the circle line goes round in a circle
Update 3: But how can it travel backwards on one line. I'm talking about in london.
If it traveled back it would crash in to the normal train
Update 4: i know they have driver seats at both ends i'm talking about the TUBE LONDON UNDERGROUND
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