The best supplements I seen for adjudicating terrain in any type of campaign are the three environment books written by J Andrew Keith published by Game Lords in the 1980s. While written for Traveller they are generic enough to be used for any game system. Of the three like the Mountain Environment. It has a simple but effective system for representing the terrain complexity of a mountain peak.
It is easy to get lost in the details and make the experience a grind for the players because of too much detail. The way I learned to handle it is distill the challenge into a couple of key decisions that a player can reasonably make.
Most of the time it is time versus difficulty. Do we swing to the north and skirt the Dune Sea or do we try to cut across and risk sunstroke and dehydration? Do we climb the sheer cliff wall or take the exposed ridge line up to the peak? These books help in coming up with some creative choices.
To me the Old School Renaissance is not about playing a particular set of rules in a particular way, the dungeon crawl. It is about going back to the roots of our hobby and seeing what we could do differently. What avenues were not explored because of the commercial and personal interests of the game designers of the time.
What are RPGs?
A game where the players play individual characters interacting with a setting with their actions adjudicated by a human referee.
Rules are an aide to help the referee adjudicate actions and to help the players interact with the setting.
Dice are used to inject uncertainty which make a tabletop RPG campaign more interesting than "Let's Pretend".
The only thing a player needs to do to roleplay a character is to act if he or she was really there in the setting in that situation.