Roaring Maw (RM) is the sixth dungeon in the game, and it is arguably one of the most long, narrow, and tedious dungeons in the game. It is located in Scorching Wind Desert (X:648, Y:525). This Main Quest requires mob kills, item drops, and determination to be willing to subject yourself to what I like to call the torture dungeon.
To add to its annoyance, you do not get a quest automatically for the dungeon, and it can't be found by simply going to a map until a quest pops up, similar to OSI. However, this is why I'm here to help and make things less tedious!
To get the first quest for the Main Quest of Roaring Maw you need to go to Lost Highlands and talk to Gin (X:585, Y:583) to grab the quest [L52. Roaring Treasure Hunt] which requires you to defeat Bonaparte and kill 10 Bath Stone Guards, 10 Ruined City Keepers, and 5 Ruined City Sorcerers. No quest item needed for this quest. Once you finish the quest, turn it in to Mystical Treasure (X:272, Y:304) inside the dungeon.
Then you'll travel to Prince Caputo (X:106, Y:35) in the dungeon for the next quest [L53. Roaring Forgiveness] This quest requires you to defeat Sahdos, collect Casper's Soul, and kill mobs. Once you finish the quest, turn it in to Prince Casper (X: 215, Y:573) he will then give you [L54. Roaring Peaceful Ending] in which you need to run back to Prince Caputo to complete the Main Quest.
Side Note: You only have to defeat two bosses inside this dungeon for the Main Quest. There are two additional bosses in the dungeon, Cyrus and Nadaphas and only need to be killed for the Mission Order. Both of these bosses are found by grabbing two different sets of keys in the dungeon and going through treasure boxes to get to them. The Mission Order title is Roaring Maw Raider (Critical Attack +10%, Defense -10%)