Drill straight through the center of the Earth from Sydney, Australia and you'd surface on the exact opposite side of the planet — its antipode.
Sydney's antipode sits at 33.87°N, 28.79°W, in the northern hemisphere, west of Greenwich. That places it in or near the Atlantic Ocean.
It lies roughly 20,015 km from Sydney — about as far apart as two points on Earth can possibly be. And the relationship is symmetric: the antipode of that spot is, of course, right back here in Sydney.
Sydney's antipode falls over open water, in or near the Atlantic Ocean — water covers about 71% of the globe, so antipodal land pairs are rare. The nearest named place is Ilhéu da Vila, a small island in Portugal, roughly 474 km away.
Antigea's live map shows the satellite view, the closest Street View, and the local time on the other side of the world.