[myleshenderson]

My grandfather gave me a puzzle when I was 8 or 9 years old where the goal was to trace a path through each of the "walls" in the diagram below without the path crossing itself:

  ---------------------
  |        |          |
  ---------------------
  |    |        |     |
  ---------------------

I played with it off and on for years and suspected that it was impossible. I realized that it is in fact impossible when I took discrete mathematics in college and we covered the Seven Bridges.

I've passed this on to my kids but only let them play with it for hours until revealing that it's not possible and getting into the theory of it.

I don't think my grandfather knows this is impossible, and I haven't yet remembered to tell him.

[Stratoscope]

In fact, this five room puzzle is mentioned in the Königsberg article and also has an article of its own:

https://en.wikipedia.org/wiki/Five_room_puzzle

Your grandfather would likely enjoy discussing it with you!

[cjauvin]

Wow thank you! So I just learned the proper name of this "puzzle", which my father also showed me a long time ago (and for which I used to fill pages and pages of trials even though I knew that it had no solution), and which I tried to render as an "applet toy", a couple of years ago on my blog (see my other comment below).

[TuringTest]

It's interesting that there exists a solution (shown in the Wikipedia article), if you build the rooms on a torus. That would be the equivalent of digging a tunnel between two rooms.

[NotSammyHagar]

Do it before it's too late. I used to have fun discussions with my grandparents about so many things. Then one day, well, they pass.