The Abbe dug all the way to Dantes' cell?

Yes, he dug all the way into Dantes' cell.

In a moment that part of the floor on which Dantès was resting his two hands, as he knelt with his head in the opening, suddenly gave way; he drew back smartly, while a mass of stones and earth disappeared in a hole that opened beneath the aperture he himself had formed. Then from the bottom of this passage, the depth of which it was impossible to measure, he saw appear, first the head, then the shoulders, and lastly the body of a man, who sprang lightly into his cell.