I am intereseted in your “sort-of per-vertex ambient occlusion” is it in a shader?? I would really like to utilise some of that tech. for my cave or more likely in other future projects,. any pointers?

From looking at the screenshot, it looks like he’s using darker colours for vertices which have higher vertices near them, so the colours can be computed from the height-map =)

yep, more or less as LunarCrisis explained – suitably simple for a 48hr game, but with quite nice results