I've coded up a little grid based dungeon game. Everything working quite nicely in a Tile[,]. The AI uses basic GOAP for tasks and A* for moving around. Tile reachability is done using a floodfill.
Thinking about what my next step would be, I decided to change the art style from being the typical dungeon to a more sci-fi approach and thought it'd be great to have multiple levels.
This is where I ran into a problem because A* in a 2d grid I understand. But adding extra levels makes it a wee bit harder. My initial thoughts would be to add connections to the next levels in 'stairs' or 'elevator' tiles and adding these to the neighbor list of a Tile for evaluation by A*.
But this throws my heuristic for a loop. I'm using Manhattan distance.
TL;DR: How should I improve my heuristic for multi level path finding?