By saying 'You won't believe how nice the plateaus look,' the speaker means that the plateaus in Goa are exceptionally beautiful and impressive, surpassing expectations.

She is expressing that the scenery is so stunning that her friends would find it hard to imagine or believe without seeing it themselves. The phrase conveys her excitement and wonder at the unexpected beauty of the landscape.

The phrase 'you won't believe' is used to emphasize that something is extraordinary or surprising. Shaana uses this expression to convey her amazement at the beauty of the plateaus, hills, and beaches in Goa.

She wants her friends to understand that the landscape is more beautiful than words can describe.