After hours of walking through the snowy woods Jones finally found the building in the middle of nowhere. He opened the main door and went in. He was in an empty space facing two rooms with closed doors in front of him. Then he saw a Tape Recorder in the corner. Freezing and shivering he turned the recorder on.

Welcome Dr. Jones. I applaud your toughness getting here. You have found the place with the Egyptian Treasure. Congratulations.

There is a small challenge though Dr. Jones. The treasure is in the back of the building and to get there you MUST go through one of the two rooms in front of you. Once you are in a room the door will close behind you and you must go to the other side of the room and open the back door to get to the space with the treasure. Simple, right?

Except, Dr. Jones, ONE of the two rooms is plumbed nicely for a delightful concentrated acid shower. Walls and ceiling have small holes which will drench you with sulfuric acid as soon as you start walking through the room. Nice eh?

Now I am a decent person Dr. Jones. So I have made the other room safe. You can just walk across. However both rooms look exactly the same. Same walls, color, even the small holes. You are wondering which is which, but I am sure with your talent you can figure that out. Oh, and if you have thoughts of just opening the door to take a look or smell, forget it. You can only open one door. As soon as you do it the other door gets locked. Also the showers are triggered by multiple sensors, not just weight. Good Luck Dr. Jones

Jones badly wanted the treasure. He had no protective equipment against the acid. He did not know how long the room was so even fast running could be risky.

After some thought he decided to do it. Why?

  • $\begingroup$ Are both the doors leading to treasure ? $\endgroup$
    – Mitu Raj
    Commented Nov 29, 2017 at 14:13
  • $\begingroup$ YES they both do MITU RAJ $\endgroup$
    – DrD
    Commented Nov 29, 2017 at 14:22
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    $\begingroup$ Why Egyptian treasure in a snowy place? $\endgroup$
    – justhalf
    Commented Nov 29, 2017 at 19:12
  • $\begingroup$ Are you spoiling the upcoming Indiana Jones movie? $\endgroup$ Commented Nov 29, 2017 at 20:12
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    $\begingroup$ Seems like OP never lived in a place where it didn't snow the whole year, justhalf... $\endgroup$
    – ffao
    Commented Nov 29, 2017 at 23:55

10 Answers 10


Not sure if this is the direction to go, but

According to Wikipedia, sulfuric acid has a melting point of 10 degrees Celsius. Since Dr. Jones was walking through a "snowy forest" and was "freezing and shivering", I'm assuming it's (almost) equally cold in the rooms. Thus, he can't get a sulfuric acid shower since it's too cold for liquid sulfuric acid.
Note that this leaves the problem that when choosing the wrong door, the door with treasure gets locked. But I guess it's now 50% treasure and 100% survival, as opposed to 50% chance of treasure and survival and 50% chance of death. As noted by Ctx, it seems that both doors lead to the treasure so this is not valid anymore. Upon rereading the OP I completely agree with this. This was also confirmed by OP.

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    $\begingroup$ But we don't know what's the temperature INSIDE the building (as far as we know, it could even be hot...) $\endgroup$
    – Hunter
    Commented Nov 29, 2017 at 14:16
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    $\begingroup$ I have another objection: why couldn't the acid be pre-heated at an appropriate temperature to avoid freezing? (in real life is maybe impossible to take a shower if the room temperature is below 0 but the water is not?) $\endgroup$
    – Hunter
    Commented Nov 29, 2017 at 15:14
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    $\begingroup$ Also, who would want to be nicely coverd in sulfuric acid snow which then will start to melt? $\endgroup$ Commented Nov 29, 2017 at 17:13
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    $\begingroup$ @Hunter This is of course possible, but shouldn't we stick to the clues we have? These say, that it is very cold, also when Dr. Jones is already inside the building. I do not see anything hinting, that the acid may be preheated. And if you read carefully: The text states After some thought he decided to do it. Why?. This doesn't necessarily mean, that he was right, we just provide the reasons here, why he was willing to take the chance! Did anyone talk to him recently? ;)) $\endgroup$
    – Ctx
    Commented Nov 29, 2017 at 17:38
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    $\begingroup$ @Ctx: Sulpheric acid expands when it freezes. Heating the tank is a practical necessity in this environment. $\endgroup$
    – Joshua
    Commented Nov 29, 2017 at 19:00

I very much like the answer of Lolgast, but I also want to propose another solution:

Dr. Indiana Jones risked his life for important archaeologic findings since he was a little boy:

  • Cross of coronado
  • Ark of the covenant
  • Sansara Stones
  • The Holy Grail

The chances to survive these adventures were way lower than 50%.

Dr. Indiana Jones really badly wanted this treasure and he didn't have any clue from outside on which door to open, and even after that, if he is doomed or not after entering the room. So he thought to himself:

  • This treasure BELONGS IN A MUSEUM!!
  • the chances are better than ever before,
  • and at least, he wasn't threatened with snakes! (phew!)
  • and maybe he even hoped that his chances rise slightly above 50% considering the acid might be solid at that temperature. But I bet he would have tried anyway, even with summer temperatures!

He hadn't slept a night from that on otherwise if he hadn't tried! That's my hero! (besides Thor, of course! And now all)

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    $\begingroup$ A true Indiana Jones Fan!!! $\endgroup$
    – DrD
    Commented Nov 29, 2017 at 19:29
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    $\begingroup$ or he could simply take cover in a fridge $\endgroup$
    – Ewan
    Commented Dec 1, 2017 at 10:50
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    $\begingroup$ Indiana Jones knows he's a main character and that dying to a lame acid trap is too anticlimactic, hence he knows he's in no danger. $\endgroup$ Commented Dec 1, 2017 at 11:19
  • $\begingroup$ @MaciejStachowski: Maybe if Ryan Reynolds was playing him. $\endgroup$ Commented Dec 1, 2017 at 11:31

The treasure is in the back of the building

Dr. Jones can use the outside of the building to go to the back, since he has to cross the room and open the back door to get to the space with the treasure, he can go out and try from outside.

  • 1
    $\begingroup$ I thought of posting this same answer but then saw the all-caps "MUST (go thru one of the two rooms)" and decided not to. $\endgroup$ Commented Nov 29, 2017 at 18:46
  • $\begingroup$ Maybe when inside the building he must use one of the rooms $\endgroup$
    – yass
    Commented Nov 29, 2017 at 18:48
  • $\begingroup$ True. Now I'm leaning in favor of this answer. $\endgroup$ Commented Nov 29, 2017 at 18:50
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    $\begingroup$ After all no knowledge Tag $\endgroup$
    – yass
    Commented Nov 29, 2017 at 18:53
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    $\begingroup$ After pointing out the necessity of the heated tank I lean towards this answer too. $\endgroup$
    – Joshua
    Commented Nov 30, 2017 at 5:09

I assume the villain is absolutely trustworthy, as the villains usually are :-)

Indiana does not risk his life (nor his limb), so there is no reason not to try. He opens one door, and shoves a heavy block of ice inside. If the acid rain does not start, he's OK. If it does start, well, he can try alternative approaches (the roof, the backyard etc.), or, just wait until the acid tanks are empty. If necessary, shoveling snow and ice inside to keep the sensors on (the reaction with water is exothermic, so the snow will keep melting). Just beware of the fumes.


The evil villain is a pretty smart guy. He was able to set up a locking system such that if one door opened, the other would lock. He put many undetectable and undisarmable sensors that would trigger his sulfuric acid trap. He built acid trap out of the correct materials, he even used a super-battery in the tape recorder, so that no matter how much time went by, it would still be charged.

There's really nothing the villain hadn't though of. Except:

The super-eruption of Yellowstone National park, which caught everyone off guard. In the few years after its eruption, the world has cooled significantly, making it so that these Egyptian ruins now experience freezing temperatures and snow. Dr Jones feels quite confident that the evil villain did not put a heating mechanism in the building, so there is little doubt that the expansion of the acid as it froze has caused damage to the trap mechanism itself.

Dr Jones gets his treasure.

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    $\begingroup$ Sounds contradicting: An evil villain that thinks of everything (even the super battery for the recorder) on one hand, the same villain forgetting to install a heating mechanism for the traps to work on the other hand. $\endgroup$ Commented Nov 30, 2017 at 0:48
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    $\begingroup$ @ibrahimmahrir I think Carls answer is based on the premise that when building the complex, the eruption hadn't occurred yet and the temperature in the region was much higher, so there would be no possibility of freezing $\endgroup$
    – Lolgast
    Commented Nov 30, 2017 at 12:03
  • $\begingroup$ @ibrahimmahrir cleverly solving one (or a handful of) problems does not mean that you've solved all problems. But, for the purpose of a puzzle, you are right, the answer shouldn't rely on "the villain just happened to forget this one thing that he could've thought of but didn't" $\endgroup$
    – Flater
    Commented Nov 30, 2017 at 15:55

My answer depends on the following:

ONE of the two rooms is plumbed nicely... However both rooms look exactly the same. Same walls, color, even the small holes.

Therefore, Jones may be able to successfully differentiate between the rooms by

putting his ear against the wall of each room and banging his fists on it. If only one contains hundreds of tiny pipes he should be able to hear their vibrations.


Indiana Jones probably wouldn't have used fair play.

Bring 2 blocks of C4 with you.

  1. Cause 1 door to close without going in, and if you see the sulfric acid coming down. Use the C4 to blast door #2. Else if no acid came down you can go in and claim the treasure. You have a spare block of C4 just in case something else goes wrong.

  2. Also he could take the door off its hinges, if present. He could also attempt lock picking.

Sulfuric acid is no good on some plastics.

  1. Use an umbrella with the right plastic and unless it comes from all directions you could be protected.

  2. A full plastic rain suit would also work pretty good.

  3. Taking a giant vase, and put it over your head. (make eye holes)

  4. Use blocks of ice(or stone) to wedge doors open.

  • $\begingroup$ I thought "plastic shielding" too. This answer is in keeping with the character and physics, and it makes the villain seem less inept. $\endgroup$ Commented Dec 1, 2017 at 8:17

Person who left the message, mentioned that there are many detectors with weighting scale included. Suppose that design was to avoid situation when Dr. Jones pushes for instance big block of rock or wooden log etc to see if the mechanism will trigger and then escape alive. So the triggering logic should be something like: TRIGGER <= MASS AND INFRARED AND LAZER AND ...etc. So, to avoid triggering he can simply avoid weighting scale to take measure. He can for instance force it to stuck or use attachable line to "swing in"...

Of course I appreciate Lolgast's answer most!


Could it be this?

"Walls and ceiling have small holes which will drench you with sulfuric acid as soon as you start walking thru the room"
So if he runs he is ok! He said he had advanced sensors and all!

  • $\begingroup$ He should rather traverse the room rolling over the floor laughing. $\endgroup$
    – M.Herzkamp
    Commented Dec 1, 2017 at 11:36

Well perhaps,

assuming many others have tried the feat prior to Jones, the ducts and nozzle must have been deformed(due to corrosion over a long period) to propel out acid with force, thereby leaving a thin space on the floor, on which Jones can carefully tread leading to the backdoor.

Hence Dr.Jones can try his option of taking a chance.

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    $\begingroup$ Given the recording specifically welcoming Dr. Jones and the wording in the message, I think it's safe to assume the rooms are fairly new. $\endgroup$ Commented Nov 29, 2017 at 17:07

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