What continent does not touch any other continent?

Only Australia and Antarctica do not have land borders with another continent.

North and South America are separated from each other by a manmade waterway, the Panama Canal, but not on the continental divide. Africa is separated from Asia by another manmade waterway, the Suez Canal, which likewise does not actually separate continents (at least not to the extent that a person could not walk from one to the other in a few steps).