2D to 3D coordinates


Wanted to reword this. I have a 3D terrain, but I view the terrain from a tilted perspective.

I wish to make it so users can click to move, but I don’t think selecting is what I want ( because I don’t want my users to always be in the center of a tile, I want them able to move around fluidly ).

Does anyone have an advice or know of a set of functions I can look into to try and do this ? I’ve tried gluUnproject, but that does X & Y , which even though is nice, I actually need X & Z to know which location they are moving to.