+Ken H kicks off the discussion with a post about simplified Swords and Wizardry and +Chris C. follows up with his own thoughts over on the Clash of Spear on Shield. Ken is musing over a low magic campaign where the fantastic elements are confined to a megadungeon, Monteporte in his case. Monteporte would be set in a medieval world with societies and technologies similar to own Middle Ages. Character would be limited to classes like Fighters and Thieves where their abilities make sense in such a setting. And do all this with a ruleset that is light on the mechanics.
From around 1987 to 2008, GURPS was THE system I used to run campaigns with. One of the main appeals was the ability to fine tune the character don't only to the genre (Fantasy in my case) but to the specific situations and tone of the campaign. GURPS made it easy to run a campaign where everybody with a magic-user. And each of them was different despite sharing common abilities. The same with the city-guard campaign, and the thief campaign.
GURPS made this easy for me by having tons and tons of lists for skills, advantages, powers, etc. Yeah it took a little work but I thought at the time a lot less work than if I had to roll my own stuff.
That proved not to be true.
It came together for me after I read Matt Finch's A Quick Primer on Old School Gaming. His assertion of rulings not rules made me realize an essential truth about tabletop roleplaying; that rules are tools and that they are not point of the game. Unlike my situation in 1987, in 2008, I was married, had kids, had over 15 years of LARP experience, and written a few published RPG books. I had a lot more life experience, all of which I can bring to bear to adjudicate the crazy shit the players do like throwing milk in a barbarian's face.
As part of the process of writing my first independent project, the Majestic Wilderlands, I had to decide what made the Majestic Wilderland, the Majestic Wilderlands. Then came the tricky part of modifying Swords & Wizardry into reflecting reality of my setting. Go too far and become a completely different game. Don't do it enough then is it really of any use as a rule supplement?
The result was a series of tweaks to the Swords & Wizardry, mostly in the form of customized classes. One major addition I made was to add an ability system that allowed characters to be better at non-combat actions over other characters. Normally they are called skills but because this is Swords & Wizardry where any character can attempt any action, I elected call them abilities as any character of any class can attempt to use them. The abilities proved to be what I needed to successfully adapt how I ran the Majestic Wilderland under GURPS to Swords and Wizardry.
So what it would take to adapt Sword and Wizardry a very low magic campaign?
The first major consideration is healing. The minimum would be that the referee needs to consider how to manage the flow of time in the campaign. Most DnD edition allow the character to be fully healed with two to four weeks of rest. If there is nothing else happening a referee could say "OK you rest for four weeks it cost the party 100 gp for upkeep and now you are fully healed". That is a little bland and it might be better to spice it up with some downtime activities. While the 5e DMG addresses this issue, it was recognized long ago, In 1980, Midkemia press had a whole section on downtime events in their Cities Book. They have a PDF available.
I strongly feel that non-combat abilities need to be quantified and distinguished. It doesn't need to elaborate like GURPS or Runequest but there needs to be something. My solutions was abilities in the MW Supplement, there are others out there that work as well. I don't feel that relying on attribute checks is enough.
Finally I found that players like variety, and choices. One easy way to do this is to have mechanically detailed characters and a straightforward setting. A lot DnD 4e adventures and setting were presented like this. DnD 4e characters had a lot of choices in how they could fight in combat but the adventures, not all but most, were just a linked series of combat encounters.
The other way is what games like Fate and Savage World do. They mechanically simplistic but try to present rich settings to adventure in. Then of course what Runequest/Glorantha, Harnmaster/Harn, and Ars Magica/Mythic Europe try to do is have a rich setting with a mechanically detailed ruleset.
If the rules are going to be detailed, then the setting needs to have the detail. At some point I am going to tire of exploring a endless monster filled maze and want to interact with something. So variety is important.
Also we are can handle dungeon exploration different if we have to take four weeks to recover from injury. A lot of focus will be on making sure we have refuges where we can hole up for weeks at a time. Another thing to consider with more realistic healing rates is that the optimal organization would be a siege expedition. Starting with a large party at the entrance, the goal would be to establish a series of base camps into the depths of the dungeon. Stocking them with supplies and securing them. From these base camps, exploring parties would be sent out, with the best or most skilled at the deepest camp.
Another observation is one from my Majestic Wilderlands, In MW the magic-users are the most advanced wielders of magic in the setting. There are other and the main limitation is how they can or can't memorize spell. For battle magic, these other magic users have to rely on scroll and magical devices. In a campaign with low magic, the referee doesn't have to have any magic-users at all. Instead magic can only be cast from a scroll, used via potion or device. A referee that want players create magic items then you can make it as difficult or easy as he wants. Perhaps it is limited to a Scholar class with the Natural Philosophy skill.
Finally given time in a Fantasy Campaign, the character will have magic-items and there will be a point where magic is literally coming out of their ears. At that point the campaign will shift and the referee needs to be prepared for that. The only question is when does the referee wants this to occur.
To wrap this up, I think a low magic Monteport will be a neat idea. I think it will need a few new rules added to Swords & Wizardry to make it interesting over a long campaign but not to the point that you are writing a complete supplement.