I found the entire sentence: But it was a chance stumbling upon a run-down, yet functional, laboratory in his late grandfather’s home that solidified the young man’s enthusiasm for chemistry. The young man stumbled upon his grandfather's run-down (dirty or possibly damaged) laboratory by chance(accidentally). The lab was still functional, meaning it could still be used and the equipment still worked. His enthusiam for chemistry was solidified by this accidental discovery of his grandfather's lab.

You really need to provide the entire sentence for context and possibly the sentences prior to and after this one.