Dungeon Kurashi no Moto Yuusha 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.cc fastest updating comic site. The Summary is

After Killing the Demon Lord, Blum Dilmond was pursued by the kingdom and forced to leave the country. While spending days trying to avoid the assassins aiming at his neck, he suddenly came up with an idea. He could hide inside the dungeon that was once the Demon Lord’s hideout. If it’s there, then he could be safe.
Without hesitating Blum went into the dungeon, but then he met someone unexpected in the lower levels, one of his former companions with whom he fought side by side against the Demon Lord. Moreover, a maid, called Irene, who once served the Demon Lord is also there. And so since their interests happened to match, the three of them decided to cooperate together to rebuild the worn-out dungeon, working earnestly in order to turn it into their own safe paradise.