There are many secrets hidden in the world of Dragon's Dogma 2, and to uncover them all you'll need to search every nook and cranny. In Bakbattahl, the capital of Battahl, there's a huge door tucked away to the southeast past the Flamebearer's Palace.
The door is sealed by some strange magic and, no matter how hard you try, it won't seem to budge. But, it is possible to open the way.
Dragon's Dogma 2: How To Unlock Flamebearer Palace Spellseal Door In Bakbattahl
The door is actually tied to the quest “The Guardian Gigantus” which has the Arisen delivering the Godsbane blade to Phaesus. This follows on from the quest "A New Godsway," which has players hunting for 15 Wyrmslife Crystals to give to Ambrosius so that he can craft a powerful Godsway.
After handing over all the materials, Ambrosius will give you the Empowered Godsbane Blade, which you must now take to Phaesus. Follow the quest marker and it will lead you to the Flamebearer Palace Spellseal Door. A short cutscene will play that shows Phaesus moving through the door and continuing on further afield. You'll then be able to follow him as the door will now be open.
Need more guidance for Dragon's Dogma 2? Check out whether you can start a new game, or where to find the Jadeite Orb.