Stuck in Orobas Fjords

I can't get through a cave in the Orobas Fjords.

It's the cave with the book for my alchemist, near the fortress with the levers to disable the force fields at the start of this area. There's also one of the bandits in it (Ragon, I think). Coordinates ca. (9, 27) on this map (scroll down to correct map).

When I enter the map I find the body of a dead priest and a key nearby. No idea what the key does.
Slightly down the path theirs a big group of bandits. The cave splits there: The path to the left leads to a locked door with a gate. I can't get through the gate.
The right path leads to a force field. I can see what's behind it, but I can't get through.

I could use some help here.

Is it this cave?

You have to activate the floor panels in the correct order (where the chest was), and that should do it. If memory serves me correctly and if those comments are correct, that is.

Yes, that's the cave. The problems is that I can't get through door 2. The panels are behind that door.

According to a guide on GameFAQs, you need to get a key from someone named "Sura", who is supposed to be in the first wave of bandits you killed. Did you loot every corpse?

Yes, several times. No Sura, no key.