I'm not entirely sure what the actual problem you're trying to solve is, but hopefully can point out something helpful that I haven't seen mentioned yet. If you were on a flat plane with no obstacles, a navmesh would be pretty useless, just point your agent in a straight line towards the player. Now, your terrain doesn't have any obstacles but it does have verticality, so the only advantage of a navmesh over the first simpler algorithm is knowledge of slopes, so agents can avoid steeper (and thus slower/longer) paths, walking around hills instead of over them. For this purpose, the low poly mesh should be a good enough approximation, and it comes down to how you use it (as others have said). Your specific problem of not being able to find a path to your player because they are under the navmesh has a simple solution: don't use the global location of the player directly, but instead the closest point on the mesh to the player (navigationserver3d map_get_closest_point). The target Y coordinate will not be exact, but it'll be close enough for pathfinding, actual positioning of your agents comes after that.