Cool ! I can help you with it if you want !
Here is the first step. Spain is know to have half-arid climats so I made it so the red parts of the flags are very hot.
You know that the more you move, the more heat your body is generating, right ? Well if you walk too much on these grounds, you die of an heat stroke.
https://www.puzzlescript.net/editor.html?hack=07149d221a8ebc02026983a2016001d2