Reimian Empire

Ah, yes. We can also try the eastern path then.

After the fog, turn left, and you can go south to reach the potion; there's a similar barred gate there, just like on the other side.

Added 1 minute ago
Although, if there's a descent into the basement, maybe it's still worth checking the western treasure room first. It would be great to find a golem there that restores spirit after battle to the maximum...