The ability to take an edge (can be very expensive) that allows you to climb in some terraine where normally you have to fly. Can add on a 2 round lag to movement where you would normally have none if you were flying. There are times when fly falls off, or if you are a rager can not access an area.

Ie: Like up to the green dragon in the weald, Xart lair, etc. Not sure why you cant train yourself to be a climber.

Play a thief, this is already a thing. See this:

CLIMB
Syntax: Automatic skill

Some thieves have become quite adept at climbing. This allows them to travel
some places they would normally need to fly to get to. They search and find
good handholds and climb up to their destination.

See also: THIEVES