In geography, the antipodes of any place on Earth is its antipodal point; that is, the region on the Earth's surface which is diametrically opposite to it. Two points which are antipodal to one another are connected by a straight line through the centre of the Earth. Full article at Wikipedia.
Double-click on or move the original map to set a marker on a desired location. The antipode map will automatically show it's antipodal location.