Let's dig a hole so deep it came out the other side of the Earth.


Earth's surface which is diametrically opposite to the above. Two points which are antipodal to one another are connected by a straight line through the centre of the Earth, in geography it calls Antipodal Point

How it works:
If the coordinates (longitude and latitude) of a point on the Earth’s surface are (θ, φ), then the coordinates of the antipodal point can be written as (θ ± 180°,−φ). This relation holds true whether the Earth is approximated as a perfect sphere or as a reference ellipsoid.