Every child in America has heard it: dig a hole deep enough in the backyard and you'll pop out in China. It is a lovely idea, and for the entire continental United States it is wrong — not just slightly wrong, but opposite-side-of-the-planet wrong in a way that's easy to check with two lines of arithmetic.
An antipode mirrors your latitude into the other hemisphere. The mainland US sits between roughly 25°N and 49°N, so any tunnel through the centre of the Earth surfaces between 25°S and 49°S — while China lies firmly in the northern hemisphere. You cannot get there from here, geometrically speaking.
What is actually opposite the United States is the southern Indian Ocean, one of the emptiest stretches of water on the planet. The antipode of New York is open sea more than a thousand kilometres from the nearest speck of land. Chicago, Boston and Washington all come out in the same watery nowhere between Africa, Antarctica and Australia.
The one grand exception: Honolulu. Hawaii sits opposite southern Africa, and a tunnel from Waikiki surfaces in Botswana, near the edge of the Okavango region — the only US state capital antipodal to dry land.
Flip the question. China spans roughly 20°N–50°N, so its antipodes lie at 20°S–50°S in the western hemisphere: Argentina and Chile. The playground myth is geographically true — for South Americans.
In Argentina and Chile the same myth exists in reverse — children there really are told they can dig to China, and they are more or less right.
Europeans sometimes upgrade the story to Australia. Also wrong, though warmer: Europe's antipodes are the South Pacific east of New Zealand. Madrid is the continental capital that comes closest to hitting land, surfacing within walking distance of a hill in New Zealand's North Island. London and Paris both land in the sea near New Zealand's remote outlying islands — close, but you would still need a boat.
Beyond geography, the tunnel itself has issues: 6,371 km of rock, a liquid iron outer core around 5,000°C, and pressures in the millions of atmospheres. Physicists enjoy calculating that if you somehow built a frictionless vacuum tunnel through the centre, you would fall the whole way in about 38 minutes and arrive with exactly zero velocity — momentarily weightless at the far end, just long enough to regret not bringing anything to grab the edge with.
Skip the digging: type your address into Antigea and see where you would really come out.