I think indoor maps are the most difficult.
Mountains and coastlines are difficult, but there are solutions.
One is to use FEMapCreator to automatically generate a random map.
If you can create a map that is close to your ideal map, it will make your work easier.
The other is to use Tiled to cut out existing mountains and coastlines and reuse them.
You can reuse them block by block, and since there are many maps with mountains and coastlines, there is plenty of material to copy.
The last method is the mountain gacha.
In FEMapCreator, surround only the tiles you want to make mountains with red tiles, and let it auto-generate them by pressing Ctrl + R.
If you don’t like the result, press Ctrl + Z to go back.
Repeat this process until you get a good result.
// This gacha is free to play.
The problem is the indoor maps.
For indoor maps, FEMapCreator’s auto-generator does not work well, probably because there are not enough of them.
And indoor maps need gimmicks as well as designs.
Your sense of ideas is more required.
Therefore, indoor maps are the most difficult.