The Igreja de Sao Joao Batista is the small white church at the ocean end of the Quadrado. Its facade is simple, almost plain, but the position is perfect: grass behind you, palms ahead, and the Atlantic below the cliff.
Even if you do not go inside, come for the view. This is the photograph everyone takes in Trancoso, but it also gives you the clearest sense of why the village was founded here.