Journey to the Centre of the Earth · Jules Verne, 1864
How deep did they go in Journey to the Centre of the Earth?
~140km
About 140 km down, at the Lidenbrock Sea: eleven times deeper than the deepest hole ever drilled, and 2% of the way to the centre.
From the bookThe map's guessReal world
They never get near the centre. By 7 August they are thirty leagues down, about 120 km if a league is 4 km, and that is where Axel gets lost. The underground sea is a bit deeper again.
The 140 km is approximate: it is Lidenbrock's figure as remembered and rounded for this map, not a quote. The depth they pass under the Atlantic, about 19 km, is an estimate too.
Real rock at 140 km is around 1,300 °C. Verne knew the heat argument and has Lidenbrock wave it away.
See the Lidenbrock Sea