A bonus dungeon is a location in a Dragon Quest game which is accessible after completing the main storyline of the game. It is considered additional bonus content to the main content of the game and typically features special rewards, challenges, or easter eggs. The concept of a bonus dungeon first appeared in Dragon Quest V, and has appeared in each installment and remakes since.
Multiple bonus dungeons can exist within a single game, and in some cases are often added in remakes of older games. It gives series veterans new challenges to pit their skills against and gives incentives to players both old and new to buy the newer versions of the game.
Both the Super Famicom and Game Boy Color versions contain a bonus dungeon that is accessible from the Castle of the Dragon Queen after defeating Zoma. A lone Baramonster appears at the end of the dungeon, which in turn leads to Zenithia The dungeon is a cave made up of layouts from the previous dungeons including:
The 2nd and 5th floor of Cave of the Necrogond
The 1st floor of Cave Northeast of Jipang
The 2nd floor of the Underground Lake
The 1st floor of Gondo Cave
The prison room of Manoza Castle
The center of a fighting ring
In the Game Boy Color version, in Leiamland, the spot that was occupied by Ramia will become a portal to the Ice Cave, a second Bonus Dungeon. The entrance, will become available after making a wish to Xenlon to open it.
Main Article: Fungeon
The remakes introduced a new dungeon and chapter. Located beneath The Azimuth, this immense and strange dungeon featured many creatures from later games and culminated with the bonus boss: Chow Mein and Foo Yung. After defeating them the first time, a side quest starts that enables the player to resurrect Rose and recruit Psaro as a party member. The bonus bosses can be fought again to obtain special gear exclusive to Psaro.
Main Article: Estark's Labyrinth
The first true bonus dungeon is Estark's Labyrinth, which contains the superboss Estark as a cameo from Dragon Quest IV. After beating Nimzo, the player can find Estark's Labyrinth in a hidden part of the map. The dungeon is a maze-like area where Estark himself can be found. In the PS2 & DS remakes, after defeating Estark a special T'n'T board aptly named "Stark Raving Mad" can be played; if the player manages to reach the finish, it unlocks two unique and powerful monster companions.
Main Article: Fungeon
After defeating the final boss, if the party have between them reached the fifth level of every single class, including the secret classes of Dragon and Liquid Metal Slime, then they can enter the Fungeon through the back chamber of Alltrades Abbey in the Upper World. The Fungeon's name is confirmed in Dragon Quest IV (and it can be implied that Dragon Quest III and Dragon Quest IV also have the Fungeon as well) and borrows rooms from other dungeons. Besides taking the heroes to a grim mirror of Weaver's Peak, with some of the rarest items for purchase, the Fungeon is home to one of the most powerful monsters in the entire series, the demon lord who destroyed Castle Graceskull, the great and terrible Nokturnus. If the heroes can defeat him within 20 turns, the player will be treated to a very special ending variant of the final battle against Mortamor.
Cave to Another World/Cave to Yet Another World
Main Article: Cave to Another World
The seventh title features two bonus dungeons that appear once the final boss is defeated: the Cave to Another World and the Cave to Yet Another World. Both of these dungeons require their own sets of fragments to be amassed and assembled in the Shrine of Mysteries, and consist of recycled areas explored earlier in the game with more powerful monsters and greater treasures, similar to the Fungeon. At the end of the first bonus dungeon is The Almighty, who will offer the party a friendly bout after congratulating them for their undertakings. The fight at the end of the second dungeon is against the four elemental spirits: the Earth Spirit, Fire Spirit, Water Spirit, and Wind Spirit.
Main Article: Dragovian Path
The bonus dungeon is the Dragovian Path, which features a sidequest that uncovers the Hero's heritage. Getting through this area is required if you intend to make it to Dragovia and eventually take on the Dragonvian Trials.
Main Article: Heavenly Dais
The Heavenly Dais is an area that must be ventured every time the player wants to take on the Dragovian Trials. The area is a natural landscape with a prominent yellow colour and has several paths. The second area has stairs made of light which take the player to different areas, though only one route will take you to the door where the Lord of the Dragovians awaits. Before the boss, there is a giant door. Enter in and you'll find the Dragovian Lord himself.
To actually unlock the Dragovian Trials, you must defeat the Dragovian Lord. After freeing him from his crazed state, he'll thank you and tell you that can now do the Dragovian Trials. Obtaining the Dragovian Ring unlocks an alternate ending after defeating the final boss again. In the Dragonvian Trials, the player must fight against the Dragovian Lord's various forms: Vermillion Dragon, Emerald Dragon, Silver Dragon, Golden Dragon Darksteel Dragon and Divine Dragon. Once all of them are conquered, the player must fight each one in sequence (though their HP is halved) until they reach Ultimate Dragon, the strongest (or was) boss in the entire game.
Alter of Wroth
Main Article: Alter of Wroth
The Altar of Wroth can be accessed after the destruction of Neos and visiting the depths of Dragon Graveyard to talk to the sage Golding. It's presence expands on the game's story by adding in a new boss: Juggerwroth. He was sealed away in the Alter of Wroth after his master Rhapthorne was defeated.
Main Article: Memories Lane
Memories Lane is a secret dungeon that can be unlocked by the Lord of the Dragovians as a prize for completing one of the Dragovian Trials. It allows you to fight harder versions of several of the game's bosses (with the "in Memoriam" suffix) and at the very end has Estark, a recurring superboss who eclipses Ultimate Dragon in terms of difficu
Tower of Nod
Main Article: Tower of Nod
The Tower of Nod becomes available after completing the main storyline and obtaining the Starflight Express. The main boss itself, Nodoph can be awakened and battled after completing a line of DLC Quests to obtain Nodoph's Tear.
Main Article: Grotto
Considering that Grottoes tend to be more difficult than the main game, the difficulty of higher leveled grottoes may rival that of other bonus dungeons in the series. In addition, the Grottoes are always randomly generated and come with various difference appearances. They're also home to powerful monsters seen nowhere else, some of which can be slain as part of several sidequests.
Main Article: Drustan's Labyrinth
Ye Olde Reflectory
Main Article: Olde Reflectory
Though not as expansive and daunting as other bonus dungeons, the Reflectory more than makes up for it with it's selection of Mirror Bosses. It can be unlocked after beating the game once and can be locacted in Avalon. At first, the player can only fight Clank 'n' Knalc, Nomeg, Salta, King Latem and Valgirt. After defeating them, the player unlocks 3 purple mirrors containing even harder bosses: Der Gib, Nomegoen and Valgirt Nedlog. Defeating these 3 bosses unlocks the final mirror boss: Edahs 'Sohpix
Defeating Edahs 'Sohpix allows the player to unlock Payback Mode, a New Game Plus mode where the player starts the game with Xipho's sword (which can be upgraded into the Deathbringer's Shade).