I cant remember the name of a manga and I cant find it in my previously read. The plot (or a section), a boy is in a dungeon and is stuck inside and has to fight and ends up eating a monster part and getting super strong. When he finally goes to leave he ends up fighting someone and goes back in to the dungeon to get stronger in a few days. Thats as far as I remember and/or read.

Any ideas or help?

Dungeon Seeker?

Arifureta?