The Iron Wall is a hallway wall that we modified to support magnets. We use it instead of the refrigerator for magnets and it works very well. The best part is that it looks just like any other wall.
The secret is a special paint that has a high iron content. Put a few coats of iron paint on the wall and you will have enough metal for a magnet to grip. It's a weak grip but magnets don't need much to stick to the wall.