Climbing is an EFU system to travel in ways that are not supported by the base game. Climbing doesn't work in all areas. Some forms of climbing allow you to go up/down elevated ledges; whereas others allow you to cross gaps or go up/down cliffs that have been specially marked by builders.
Climbing requires a DC check to be passed to succeed. Your skill in climbing is altered by your Climbing EFUSS skill, armour skill penalties and the weight you are carrying.
Failing a climb check can result in damage being inflicted on your character (to represent falling) or, in particularly treacherous climbs, your character may fall into a different area.
Methods of Climbing
In order to access climbing, the following tools are available:
This represents climbing with just your hands and thus is the most difficult - access by using the Crafting Menu to set the relevant player tool to Climbing. Then hotkey the selected Player Tool on your hotbar for use. When along a ledge or other appropriate climbing spot, click above/below and your character will attempt to climb.
This is an item that can be found or purchased, works otherwise the same as the player tool.
Lower a rope down a ledge to climb down and be able to climb back up; note that a rope can be picked up only from the top.
Grapping Gun / Hook + Rope
Equip a grappling gun, with a rope and hook in your inventory, and use the unique power of the grappling gun to lodge a grapple at the bottom or top of cliffs. You can also use the unique power (self only) in specially marked areas to go across chasms or up/down pits (a message will usually display if you are in one of these special areas (saying 'Entering Horizontal/Vertical Climbing Zone')
Heavy but makes for very easy climbing.
Polymorph Formed / Wings
Some races and classes have access to the ability to fly. These creatures may climb using the appropriate player tool, circumventing the need for Grapple Guns / Hook + Ropes.