Modelling a landscape

This question is also connected to procedural textures but I posted it here.
I stumbled accross Mike Pan’s page http://blog.mikepan.com/page/4 where he created landscape.
There is a blend file but I would like to make my own landscape. Could you poit me to tutorials how to make niches, caves rivers with water…
Basically, I made one with plane subdivided but had some sharp edges, performence was not the best. While Mike’s looks excellent and fast rendered.

Thanks

Those blender tutorials are dealing with various type of environment, certainly going to be useful for you