[Is this the way out or a costly dead end?]

We’ve tackled all sorts of brain teasers in the past. From the Brooklyn Nine-Nine desert island seesaw to several hat puzzles, from Cheryl’s birthday logic puzzle to a diabolical light switch puzzle, we have conquered all challengers thus far!

But never before have we confronted a puzzle with as much backstory as today’s contender. Ladies and gentlemen and PuzzleNationers of all sorts, today we battle the Temple Tunnel puzzle.

Imagine that you’re a professor leading a group of eight grad students on an expedition into a booby-trap-filled temple.

[No, not THAT professor.]

After two of the students bump into an altar, they activate a trap, sending everyone scrambling for the exits before the temple collapses all around you.

The group finds itself in a room with five tunnels and an hourglass detailing how much time you have to escape. One of them leads back to the altar and the other four are possible routes of escape. Unfortunately, you can’t remember which one it is!

All you remember is that it took approximately twenty minutes to get here from the exit. How do you determine which tunnel is the correct one, and get everyone to safety?

Oh wait, there’s one more little complication. That altar the students bumped into? It released the vengeful spirits of the temple’s king and queen, which have possessed two of your students. So you can’t trust what they say.

So how do you figure out which tunnel is the right one without being deceived by your two compromised students?

[Image courtesy of XKCD.com.]

*deep breath* Wow, that’s quite a setup! So let’s summarize:

• You have an hour to escape, and four corridors to explore.
• Each corridor will require 40 minutes to explore: 20 minutes to determine if it’s the exit, and 20 minutes back to report your findings.
• Whatever groupings you break the team up into, you have two possible liars among them, and no way to determine which ones are the liars before sending them down a tunnel.

For a wonderful animated version of this puzzle, as well as its solution, check out the YouTube video below from TED-Ed:

Now, while the solution itself is quite clever, I can’t help but ask certain questions:

It says that the possessed students can’t harm the others, but can they mislead them with actions as well as words?

I’ve seen several proposed solutions that included not only sending groups down the tunnels, but instructing one or more of them to leave the temple immediately if they find the exit (meaning that not seeing them return would confirm they’d found the exit). But if the liars can simply stay at the dead end, that would be a false confirmation of finding the exit.

The video is ambiguous about this, because it says the spirits will lead them to their doom, but then it also says that the curse only affects their communication.

How does the group know you’re not one of the liars?

The solution is entirely dependent upon you being able to explore a tunnel alone, because that determines the groupings for the other three tunnels. If you have to take someone with you (either an honest student or a liar), that affects your ability to draw proper conclusions from the other groupings. And even if you find the exit, the student with you could lie about it, and there’s no way to prove the truth to the group definitively.

Why not just ask each student individually a question the ancient king or queen wouldn’t know the answer to?

Presumably the spirits of ancient royalty wouldn’t know about the latest episode of NCIS or which version of Windows we’re up to.

In any case, this was a delightful mind-bender, one that has stumped many an intrepid solver. How did you do? Tell us in the comments below!

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