From the D2:ED walkthrough;
Quote
Rory [120]: The mine is overrun and my secret pension is gone! Unless they don't find the hidden wall in the little office, then... No, I must flee or I'll die here!


In the mine there is a wall that can be removed with a lever handle that you find elsewhere in the mine, and another opened by a pressure plate (which opens a room and gives you access to a switch to open another wall. You don't need to mindread Rory to find either; it is just a hint to search more carefully.
The far eastern room in the mine has a lever socket on the floor, where you can place the lever handle from a chest to the far south in order to open a storage room with a chest and a couple crates.

Heading south from the entrance and then west, there is a room with a pressure plate on the wall to open another storage room. Facing south at the end of the room, towards some curtains, the plate is on the left. Inside the storage room (behind some crates) a switch will open another wall, and close the one you just went through; jump onto the table and you can reach the pressure plate to open the wall again.