Just to add to this, and to address some comments about skill systems (which have come from
@Crimson Longinus and
@Don Durito):
Here is the entry for Climbing skill in Burning Wheel Gold Revised (p 264):
This skill allows the character to navigate sheer surfaces using rope, harnesses and really strong finger muscles. In addition, rougher surfaces can be scaled with bare hands.
Obstacles: Easy climb (a rocky hill, a tree or a fence), Ob 1. Moderate climb (inclined rock wall, a treacherous tree), Ob 2. Difficult climb (straight rock wall), Ob 3. Dangerous climb (sheer rock wall), Ob 4. Impossible climb (ice climbing), Ob 5. Suicidal climb (bad conditions, overhangs, etc), Ob 7.
FoRKs: Knots, Rigging
Skill Type: Physical
Tools: Yes, expendable.
This is what I expect a classic simulationist skill entry to look like: it identifies what the skill bonus represents (ie skill with climbing gear and/or strong fingers); it locates it within the broader context of possible actions (this is a physical skill, and it is aided by skills such as Knots and Rigging - Fields of Related Knowledge); and it characterises obstacles that the skill might be used to overcome (like different sorts of slopes and surfaces) in game-mechanical terms (the list of sample obstacles).
A contrast could be drawn with the 4e D&D skill system, which identifies the relevant sorts of activities the skill pertains to but uses a pretty different sort of framework for establishing difficulties, and is much more open about what the skill bonus represents (eg suppose that an Epic tier Wizard has a +15 bonus to Athletics - it is really up to the player and the rest of the table to decide what that tells us about the character, and given that most of that bonus will be a level bonus there is no expectation to describe the character as having strong finger muscles).
The process of establishing a BW character's climbing bonus, and of working out what the difficulty is for a climbing attempt, strikes me as "diegetic" as that term gets used in RPG analysis: in the fiction, there is
this character with
these fingers and
this degree of mastery of rope and harness, standing at the base of
this (near-, semi-)vertical surface that poses
this degree of challenge, hoping to ascend it. And the audience is in the same sort of relationship to these game elements like the bonus and the obstacle.
Whereas in 4e D&D it is not a diegetic process. The PC has a climbing bonus, but the number on the sheet doesn't tell us a great deal about what this character looks like, or does, when they try and climb. And there is a (near-, semi-) vertical surface but its in-fiction properties are not the main consideration in determining what obstacle to set.
I don't know whether 5e D&D, as typically played, is closer to BW or to 4e D&D.