Lo-Fi Games

I'm just trying to add some cliffs to an area of the map using the in-game editor. However, when I do so the cliff can be walked through as if it weren't there, and doesn't persist after the game is reloaded. Is there a way to fix this?

The in-game doesn't automatically generate the navmesh. Use the ctrl-shift-F11 shortcut, or the 'regenerate sector' button in the navmesh tools.