BlameTheParrot
That's what I did and it worked. When I first used it, I was near the table with the chairs you move to get to the hidden room and it sent me to the portal to the left of the table. Click again and it said to go back through the same portal.
Instead, I moved to up near the castle and used LTF again. It said to go into the castle. The missing tile for me turned out to be in the center of the grey pattern in the center of the first castle room - a grey tile that blended in very well.
