Dragon Quest IV Locked Blue Door Locations
This guide is a list that contains the locations of every Locked Blue Door that you come across in Dragon Quest 4. In order to open these doors you'll need to get the Thief's Key during Alena's chapter. Or use the Ultimate Key acquired much later in Femiscyra.
If you'd like to see the locations of Magic Key/Ultimate Key locked doors, follow the links below to be taken to those guides instead.
List of Locked Red Doors (Magic Key)
List of Locked Doors (Ultimate Key)
Endor Armor Shop (Liquid Metal Armor)
These two doors have no chests behind them but what they do have is an armor shop that sells Liquid Metal Armor, some of the best armor in the game - for a hefty price of 35,000G each. If you can afford it, you should buy two of these, one for your Hero and one for your Healer.
On top of being some of the best defensive armor in the game, the armor will also reduce the damage you receive from magic attacks. In the screen shot below I am upgrading my Hero from Dragon Mail to Liquid Metal Armor.
Zamoksva (Alena's home town)
This set of doors is found on the upper floors of Zamoksva Castle, right next to Alena's room. It's a place you should be very familiar with considering the only way out of the castle on Alena's chapter was to keep coming upstairs and jumping out the wall.
Items from Treasure Chests:
Chimera Wing
Seed of Magic
30 Gold
Burland, Castle First Floor (Ragnar's home town)
You have to come to Burland twice I think throughout the game and each time you'll be passing right by this set of treasure chests. For that reason I would say these are another few that are hard to miss. Good thing too since they're filled with goodies!
Items from Treasure Chests:
Mini Medal
Iron Helmet
Seed of Life
Seed of Agility
Seed of Strength
750 Gold
Femiscyra Blue Doors in Throne Room
These two doors are almost impossible to miss while you're doing the quest in this town. They're clearly visible almost anywhere you stand on the upper floor of this castle. If you haven't reached Femiscyra yet, you'll come here when you are collecting the Zenithian Armor. This town is also where you receive the Ultimate Key ;)
Items from Treasure Chests:
Leather Dress
Seed of Agility