One time while leaving the still imprisoned Morgan (Simon Pegg), Lauren (Lily Collins), leaves the key on the table with the chess board. Morgan could have used the key to free himself.
When Lauren and Morgan are playing chess in the bunker, Lauren, playing with the white pieces, has her king on d1 and her queen on e1. The set dresser placed the king and queen on each other's starting square.
After 30 years underground, shackled and deprived of exposure to sunlight, the prisoner would be suffering a myriad of health conditions including soft bones and teeth, skin lesions, impaired eyesight, chronic fatigue, and severe malnutrition. His hair would have been longer and matted and he could not have eaten the steak dinner without getting ill.