The answer is SUBCLAVII The corresponding square is house puzzle by Brian Litofsky How'd we get that? Basically, the puzzle is an encrypted string with "subclavii" as the key. It uses a simple crytography method [ed.: a Vigener cipher, but with A indicating a Caesar shift of 1, not 0], which adds the first letter of the key to the first letter of the cleartext, the same for the second letter, and so on. If you pass 'Z', start counting from the beginning of the alphabet again. Once the end of the key is reach, start back from the beginning. (Note: whitespace and punctuation are ignored.) The encrypted text is the first paragraph of the monopoly rules, the one about the idea of the game. The line in the header "I wonder how to do this" is a suble pointer in that direction. They can either go find that and work at it that way or do more standard cyptography methods.