Earth's First Dungeon

Reginald Montgomery was a high class Rules Lawyer, specializing in the 'art' of Min-Maxing a Character.  He had been the secret behind the ability of the Guild 'Eternal Gamer' being able to obtain the World First Clears of various MMOs for the last five years.  The political entities of the world had hidden the imminent approach of a gigantic meteor, of similar size to the one that theoretically wiped out the dinosaurs, until it was able to be spotted by high powered astronomical telescopes. The United Nations sends nukes into a crater located deep on the meteor, breaking it into millions of smaller fragments, except for around two areas, where there was a building that looked like an old school Roman temple and one where there was a giant metallic cube.  The cube crashed into Reginald's backyard, and his 'gamer' senses were itching at the chance of supremely valuable loot. Upon investigating, he is injected with a control crystal for a 'Construction Core', but when it releases an extremely high density of pressurized mana, his body seizes up and the Core draws his mind into it before merging the control crystal back into the Core and retreating into the Cube and digging itself deeper. Two months later, Reginald becomes aware again, only to find out that nothing is as it was and he is now the Earth's First Dungeon...