Exit the linking bubble and go to the left. Walk all the way to the end of the beach. Turn to the left and enter the cave to the other side of the island. Walk all the way to the end. Turn to the left and walk forward until you are standing on the shore in front of the distant island. Cross the water and stand in front of the rock that is blocking your path. Wait until the rock collapses and than quickly step into the room.
Keep in mind that this only happens once. If you are too late and the rock/door re-appears before you enter the room, you have to restore the game you just saved and try again.
Enter this new linking bubble and make a note of the Bahro sign on top of the pedestal. (Big circle with 4 small ones) Press the bottom sign on the pedestal to get linked back into the first linking bubble. Take the Slate from the pedestal and make a drawing of the newly discovered Bahro sign.
Drop the Slate on the ground and exit the linking bubble. Turn to the right once more and re-enter the linking bubble. Press the newly appeared sign on the right side of the pedestal to get linked to The Keep once more. You have another meeting with Esher.