The Dragon Puzzle - One Geeky Geocache

(Nick Parlante)

This page has videos and other information about the very geeky dragon puzzle geocache.

I love the idea that you come across a mystery object with no instructions or anything. You manipulate it and look at what it does, and with luck have that Aha moment to figure out what it means. The dragon puzzle is not easy, but I hope the Aha moment is all the sweeter. Bring a piece of paper and take your time to try to work it out. There are hints if you need them.

Dragon Video

Here is a video that shows the dragon puzzle in action, walks through the same hints as the geocaching page, shows the hardware, and at the end reveals all the steps for the solution.

The original iron dragon puzzle was kind of magnificent (pictures below), made from an 8 pound cast iron dragon from Cost Plus. Its large size meant it was always hard to hide and keep dry. It was taken away and returned several times. A beautiful dragon, but causing some difficulties (it's all in the logs). Eventually it went permanently missing - Stanford cut down the tree it was hidden in. I decided to build a replacement, but it was very slow going.

For the new (2017) dragon, I focussed on making it small so it would be easy to hide. Its hardware is quite minimal: there's a bare Atmel 328 chip and wires for the switches and LEDs are soldered right to the chip socket. It all fits in a round candy tin from Trader Joe's, taking advantage of the transparent plastic part of the lid to show the LEDs. The LEDs are set to just medium brightness to keep the power use low. Also saving power, the chip uses its internal 8 Mhz clock. The chip runs happily on the 2.7-3.0 volts provided by a CR2032 coin cell. As the battery runs down, the chip keeps running perfectly, but the LEDs become increasingly dim.

The first power switch was a little fussy. I think I damaged it with too high a soldering temperature. In 2019 I replaced the switch and now it works great.

I can only think of this project as something I can hack around on just for fun. And of course it's great to read the logs as people find it. If you have the time, go visit and click around with this bit of hardware in the heart of silicon valley.

Dragon Pictures

Picture from early on. The LEDs are glued into the Trader Joe's tin with a toothpick.

Finished internals:

Dragon with sphinx, near the geocache:

The Original Iron Dragon Puzzle - RIP

Down here are my old notes and video for the original iron dragon puzzle, RIP! Also the guy in the video is a lot younger!

I've played around a little with the inexpensive and open source arduino microcontroller, and it's perfect for making a little battery powered puzzle. I've done a little geocaching, and I figured that would be a good the way to structure the puzzle -- you find the dragon puzzle at the first GPS coordinates, and you must solve the dragon puzzle to get the coordinates of the nearby treasure cache.

With these ideas in mind, I saw this cast iron dragon on sale for $8 at Cost Plus and knew I had found my mystery object. Like any project that looks good in the abstract, there were more a lot more issues than I had imagined in actually making it work.

Note the precision construction of this space-age instrument:

If you'd like to visit the dragon puzzle on Stanford campus, go to dragon puzzle page at, (you'll need to sign up for a free account to get the coordinates).

2010 Update

Here's what I've learned up through July 2010:

Video (2009)

Here's a little video I made using my laptop's camera to show how the dragon is built and how it works (spoiler alert: in the last part of the video, I show how to solve it, but you can watch the video up to that point without spoiling the puzzle). I used the new HTML5 video tag to embed the video in the page using the new, open WebM codec. From a technical point of view, this the way video on the web should work, and as a geek I'm happy to be the early adopter for this sort of thing. To watch the dragon video you'll need a browser that supports HTML5 WebM out of the box, such as as Mozilla Firefox or Google Chrome.

There's one other subtle thing the dragon does when you solve the puzzle which, it occurs to me, is not shown in the video. You'll have to visit the dragon to see that bit.

There's also a great talk to see and an inspiration for this project: JJ Abrams Mystery Box (watch the video or just read the transcript) about how mysteries drive the plot forward in Star Wars, Lost, etc. Also, the puzzle hunt at Stanford known as The Game is an inspiration from back in the day.

Of course this whole project was just an excuse for some hardware hacking and tinkering, and I hope that people who find it get a kick out of it. This project makes no sense in terms of cost/benefit of my time. But in reality, I've gotten immense enjoyment out of it and reading the logs as people play with it, so I guess everyone needs an impractical little creative project.

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Nick Parlante nick.parlante -at-