Ihoujin, Dungeon ni Moguru is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

It was in 1946 that Earth learned of the existence of other worlds. As expected, many countries immediately tried to send people into the other world, hoping to obtain vital resources or mystical treasures. None of them came back.