I remember seeing something about marking navmesh edges on the edge of clifs where NPCs can drop down a level but I can't find that tutorial again.

Any advice about that and about how to navmesh say a water filled shaft that you want NPCs to be able to drop down into and then to climb out onto a ledge?

Hi,

to create dropdowns, http://www.creationkit.com/Navmesh#Dropdowns. On the same page (a little bit above) are the hints for creating "water" navmesh.

-docblacky