Air level of the map.

Initially, I wanted to write about a ship. In that case, it might be better to make the Castle a mobile aerial fortress, and the Ship a faster but lightly armored one.

Something similar to Ilm-Hijah of Zehir? Like a flying castle, for example? That flies, lands as a small fortress, takes off, and flies further? Or does it land in the sky? Then maybe we could create magical fuel for them, so to speak, without which they can't fly?