This is a guide for the blue crystal room at Fort Dragonia in Chrono Cross: The Radical Dreamers Edition.
To deactivate the blue crystal, head north-west from the central area with the save crystal.
What to do at the Blue Crystal Room
After traversing the walkway, you’ll arrive next to a doorway with a blue switch near it. However, you can’t reach it from your current position. For now, follow the ahead path in a westerly direction. By the south-west corner, there are two chests, but there’s no treasure inside. Inspect the bottom chest and the bridge to the north will swing downwards.
Go across the bridge towards the central glasses-shaped portion of the room. Continue until you reach the north-east corner, where you’ll find a familiar sight: another pair of chests. If you want, ignore these chests. Instead, head west along the upper path, towards the north-west corner. Here, inspect the top chest to move the southern bridge back to its original position.
Return to the north-east corner and go back across the central path, which now leads to the westernmost room. But beware because a battle with a Dragoon will begin the moment you enter. After the Dragoon battle–or if you want to skip it–inspect the bottom chest by the north-east corner. This will shift the bridge to the middle position.
Afterwards, go along the upper path towards the north-west position. Inspect the chests so the bottom chest is open and the top chest is closed. This will move the bridge below so its pointing north-west, allowing you to go across it. From here, travel across the central path to the easternmost room. Inside is a chest with a Sea Charm.
To progress, backtrack to the north-east corner and inspect the chests so the top chest is closed and the bottom chest is open. This will move the bridge so it’s pointing south-east. Return to the north-west corner and go across the central path. You’ll finally arrive near the doorway you saw at the start. Inspect the blue switch to create stairs leading back to the entrance.
Through the doorway, you’ll find the blue crystal ahead. But before you reach it, the boss of this room–a Giant Gloop–will materialize.