[RPG] How to turn a B*-tree into a puzzle

This is a question of character knowledge versus player knowledge.

Cryptanalysis is a fun, if little used, human skill. Some players will delight in solving cryptographic puzzles, and 4e certainly doesn't prohibit the gamist approach of "challenge the player."

On the other hand, cryptanalysis is highly binary. People either really like it, or basically can't stand it, especially if you start branching out into some of the more interesting, but trivially solved cyphers (playfair, Vigenère).

I, unfortunately, had to learn this fact the hard way. Players, as a rule, will take one of two approaches to puzzles. The first approach I learned when I gave a cryptogram in a sci-fi game: "I hire an expert from town to solve it for me." is the general pattern here. To make this approach interesting, the cryptanalysis must have extrinsic complications such that one can't submit it to an analyst (magical or otherwise) and wait it out. Beyond that, having a player go "and I solve it. what does it say?" is absolutely valid, and should require either a pure int check, or a skill check of an appropriate skill the player is bringing to bear. I would personally recommend looking at the serious skills series to see how to make this approach more interesting, as players can add depth to their character by describing how a particular facet of knowledge was brought into play. Still, if you're not expecting it, it comes as a horrible horrible surprise. Some people just don't find puzzles fun.

For the players who find puzzles fun, especially for a 4e game, take a page from Portal.

Teach players one component at a time of the puzzle. It'll seem way too easy to you, but you know the context. For a crypto puzzle, start by teaching the alphabet. (Maybe touch the "true characters" not to get shocked) In subsequent challenges, teach the order of the alphabet. Again, always give an example of what you're looking for before you ask for what you're looking for. (Or, provide a way for rapid abductive reasoning without penalty.)

This way, after quite a few sessions, your players will be able to manipulate the language as a tool to solve problems, and may occasionally be assisted by their characters-as-characters.

An interesting touch would be to make the language three dimensional, and have the puzzles follow the rules of the game Zendo. Then the rough series of questions can be "complete this sentence." or "find the incorrect thing." Both are completely appropriate to solving a crypto-language, and both can engage players, instead of abstracting the puzzle to their characters.

This falls under the principle of include three clues for everything. It also is well suited to the approach of using environment-based storytelling.

Use Environment-Based Storytelling

Introduce the puzzle setting first and let the players be confused over the weird specificity. I like the petrified inhabitants part; maybe have the husband-farmer and wife-farmer wearing crowns, placed upon them by whatever mischevious fiend set up this puzzle. The players probably won't understand what's going on, but you can include enough detail that they will find it weird. Including a visible goal will help: a chest in the corner that's sealed with mystical force or an unopenable cellar door with the symbol of an inverted crown on it.

Once the players' curiosity is piqued, they will probably resume exploring. Here is where you can include your clues: a mocking poem in the children's room about farmers becoming kings and queens and a horse becoming a knight, a chess set out on the table in the parents' room with only three or four pieces on it, and so on.

Provide Many Clues

Even if you include what feels like too many clues, your players won't notice. They'll find just enough clues to figure out the solution, and then they'll stop looking. Even if you include an extra clue, they'll feel clever and excited that they already know how to interpret that. In the worst case, if they figure it out immediately, just leave out any remaining clues as if you expected them to get it quickly.

As far as worrying about being too obvious: your players have a lot on their plates. They're visualizing a world you're describing, balancing resources, and keeping in mind their larger goals in the world. Picking up on even obvious clues is enough of a challenge. Recognizing that the "king" and "bishop" in a message refer to chess pieces seems obvious in planning, but it's an impressive leap for a player who's already juggling a bunch of other knowledge.

Conclusion

As long as you don't have them find a note that says "THIS IS A CHESS PUZZLE AND HERE IS THE SOLUTION," you're probably not being too obvious.

As for being too esoteric: have a backup clue that stops just short of the obvious note above, and if it seems like they're moving on without solving the puzzle, place it in the next place they look.