by Anaesthetic
One possibility is to place the deck of tiles next to the starting chamber (on one of the sides where the starting tile has a complete wall), and to place the gem tile on the opposing side. These two spaces are unavailable for exploring or entering for the entire game, so the game becomes a little harder.Set up will look a little like this beautiful illustration here:
_ D
S S S
_ G
Starting tiles, Deck, Gem tile