I assume it is based on fact more or less.

Eh. Films like The Great Escape do take liberties for the sake of timing and to factor in Steve Mcqueen but are (imo) a decent summary of the source material. The 1950 book of the same name, on which the film was based, which is well worth a read and details the mining techniques in 'the great escape' and other escapes much more detail. The mining methods were very sophisticated for 'a company of amateurs', but collapses of the tunnels (often fatal) and other failures were fairly common, which isn't shown in the film so much, for better or worse.