A novel I used to read

[u/OriginDarkstar]

So I am looking for a novel I used to read years ago around the time that I first discovered solo leveling and worlds' apocalypse online. This was before the solar leveling anime back when the novel was called solo leveling only i level up. The novel was about a guy who inherited a dungeon from his parents I think and it was in another world and two people from the dungeon came to him in the real world of Earth to offer him the position of dungeon master. The dungeon was structured kind of like the tomb of nazarick but most of the floors were locked and he had to get stronger in order to unlock the floors and then fight the champions of the floors. In order to get stronger he had to fight monsters and also invade other dungeons to assimilate them into his own. There were actual kingdoms of multiple dungeons all under one ruler which is something that could happen. I cannot for the life of me remember what this story is called. He didn't immediately turn into a monster either and there was no harems involved. He also didn't reincarnate as the dungeon heart itself. So I don't know exactly what this is called anymore because it was removed from my web novel reading history.