In the next part, the secret wall is in the east wall. Once you get through, you will see a chest on an island that contains a Hermes. The next passageway is in the south wall. Going all the way down leads to nothing, so feel your way down the east path. Then head north up the stream and into the next area. This room is pretty straightforward, but at the top of the stairs go right into a room with an Ether1.
The room on the left contains a save point, so save, but do not use a Tent. Afterwards, go right and up the stairs to get to the back of Baron Castle.