There's one room in every dungeon level with a tent and a book (read prompt appears). Read them all for the achievement to pop.
Do note some levels might have warped rooms that have a different look than the one you entered (you're in desert dungeon but one room is from the forest). These do not count as the book you were supposed to get from that level. Sometimes I've only had that room to be warped.
Golem, forest, desert and tech dungeons have three books each. Most likely you will get the achievement after tech dungeon level 3 once you've opened the book.