Abstracted from Bill Bryson's A Short History of Nearly Everything.

The deepest hole ever dug was in Russia, on the Kola Peninsula, near the border with Finland. It was 12,262 metres deep, which is about a thousandth of the way to the centre of the Earth. At the bottom, the temperature was 180C, much hotter than expected. It was also very wet down there, another surprise. Despite its depth, it reached only a third of the way through the crust. If someone ever did manage to drill a hole to the centre of the Earth, it has been calculated that it would take about 45 minutes for anything dropped into it to reach the bottom.