Step inside, and you will find a room with a bed and another door beyond. In these larger rooms, only one door is visible, and it will take you further into the center. Both of these rooms lead to a larger room above. The dwarf in the left room indicates that the Dragon Queen is close to dying, while the dwarf in the right room says that she will lay an egg in exchange for her life. It doesn't matter which door you choose, as both will lead to roughly the same kind of small room with a single occupant. To truly investigate the interior, you'll need to unlock one of the doors near the bottom.

Stand on the pattern in the ground where the light shine upon it for a TinyMedal / Small Medal. That is a hint for the first bonus dungeon. The woman there will tell you that the heaven can be reached from here, but only a hero can go there. Without unlocking any doors, all you can do is walk around the exterior, which includes two pools and a design on the floor near the top.

They will identify the castle as belonging to the Dragon Queen. When you enter the castle, you will be greeted by two… horses.

Castle in the darkness troll sword