Le Trou

Le trou is a movie starring André Bervil, Jean Keraudy, and Michel Constantin. Distrust and uncertainty arise when four long-term inmates cautiously induct a new prisoner into their elaborate prison-break scheme.
Four prison inmates have been hatching a plan to literally dig out of jail when another prisoner, Claude Gaspard, is moved into their cell. They take a risk and share their plan with the newcomer. Over the course of three days, the prisoners and friends break through the concrete floor using a bed post and begin to make their way through the sewer system -- yet their escape is anything but assured.