Fort Dragonia: Blue Crystal Room

You'll start off on a walkway. Head west until you reach the south-west corner. You'll see two chests here, but don't worry about treasure in them just yet. Inspect the bottom chest. This action will cause the bridge to the north to swing down, opening a path for you.

Cross that newly positioned bridge and head towards the central, glasses-shaped part of the room. Keep going until you reach the north-east corner. There are two more chests here – you can grab them if you like, but they aren't essential for the puzzle. Instead, turn your attention west and head along the upper path towards the north-west corner. Here, inspect the top chest. This will move the southern bridge back to where it was originally.

Now, make your way back to the north-east corner and cross the central path again. This path now leads to the westernmost room. Be warned, though: as soon as you enter, you'll be thrown into a battle with a Dragoon. After that fight, or if you want to bypass it, head back to the north-east corner and inspect the bottom chest. This will shift the bridge so it's in the middle position.

Next, go along the upper path again, heading towards the north-west. Make sure the bottom chest is open and the top chest is closed. This will adjust the bridge below so it's pointing north-west, letting you cross it. Once you're across, take the central path to the easternmost room. Inside, you'll find a chest containing a Sea Charm.

To finally progress, you need to head back to the north-east corner. Here, inspect the chests so that the top chest is closed and the bottom chest is open. This will rotate the bridge so it's pointing south-east. Now, return to the north-west corner and cross the central path. You should now be able to reach the doorway you saw right at the beginning. Inspect the blue switch next to it to create stairs that lead back to the entrance.

Go through that doorway, and you'll see the blue crystal. But before you can grab it, the room's boss, a Giant Gloop, will appear!