Escaping the Nuclear Fallout Shelter that has Turned Into a Dungeon Alone

There is only one person inside the nuclear shelter, and inside it, the hibernating protagonist had just awoken. The world he had woken up to is one where 100 years have passed, becoming a different world altogether. The nuclear shelter that the protagonist was living in had been affected (TN:by radiation?) and transformed into a dungeon. The protagonist received a mysterious message to download a program called Adept System, and using it, he is able to absorb magic essence while gaining levels. Magic essences can be obtained from defeated monsters. Utilising the nuclear shelter self-defense system to kill monsters, the protagonist takes on the challenge of escaping the nuke shelter.