Looking for a manga

It was about dungeons that pop up randomly. The main character joins a guild to search for the treasures that appear in the dungeons. I think the boss of his guild wanted to get rid of him so he could get his treasures. He sends him to a really tough dungeon and he ends up dying. I think he gets a chance to relieve his life before he joined his guild or to when the dungeons first started appearing. Does this sound familiar to anybody?