He Who Reached 30th Floor

For adventurers, dungeons were treasure troves—mother lodes of valuable things. Dungeons were places where any registered individual could procure resources without the risk of dying due to the mysterious power of the dungeon. 

Adventurers ventured inside the dungeon in order to hunt demanded monsters for their precious parts in exchange for gold. Even though dungeons were abundant with unlimited monsters, the rare monsters were rarely encountered in Guardian Rooms, so there were types of monsters that could be seen outside, on the surface. 

Not only were dungeons veins of resources, but dungeons could be utilized as training grounds for anyone who wanted to become stronger. Dungeon crawlers could let themselves run wild and commit a killing spree as the dungeons could produce countless waves of monsters, unlimited source of EXP.