Terrain - cave path, castle overlay, lit

[white_haired_uncle]

I can do a cave path+lit or a cave path+castle overlay in the map editor (which I'm very weak with). But can I do a cave path + castle overlay + lit?

[beetlenaut]

Terrains only support one base and one overlay, so you can't put an lit overlay and a castle overlay on the same hex. To do this, you would have to make your own lit-castle terrain. You could combine the graphics for the two overlays in any decent image editor, but you would also need to define the terrain and its graphics in your add-on. (Several mainline campaigns do this. SotA is one of them.)

[Duke_Anax]

I'm not entirely sure what you are trying to do, and there is no default way to get a lit cave path castle, but you could use lit on any other existing castle.
Here is an example with a troll encampment with troll keep and an orcish castle with an encampment keep, the caverns use dirt floors.

[Celtic_Minstrel]

You could combine the graphics for the two overlays in any decent image editor,

…why would you do this? Just use both sets of graphics for your custom terrain.

But in this specific case it's even easier, because one of the sets of graphics is nothing (except for the editor overlay), so you can pretty much just make a copy of the castle overlay terrain, add the lit attribute, then make a copy of the lit overlay graphics, and modify the latter to point at your new lit+castle overlay terrain.