There are all sorts of stamps showing maps throughout the world, take a look here. The challenge is simply to create your own set of stamps with a map theme. I'd suggest four stamps in the set, but it's up you. It should be more than one, anyway. The stamps can be of a real world place, or they can be of a fictional/imaginary realm, but they should be of different monetary values, and look like they're part of the same set.

For example, each stamp could show a different region within a country. Or, you could have one stamp showing a country map, then another with a city map, and perhaps a third with a famous building. Bonus points for working in some world-building info, like who's the current ruler, or what trade/exports the area has etc etc.

If you've ever had a hankering to redo the postage stamps in your country, or to create some Middle Earth or Minecraft-themed stamps, now's your chance!