Gathering Resources
GURPS Lite 4e and GURPS Lite 3e get you the basic rules. I include 3e partly because it gives you a few more weapons and armors to work with and partly because it provides the framework from which to build our magic system. You can use GURPS Update for guidelines on things like how to change the listed ST for beasts of burden purchased in 3e, dropping Passive Defense from armors, changing pricing and/or effects of some of the traits, and so on.
Remember, there is no rule dictating how detailed your notes for your own gaming table can be - go ahead and write your own book basically, as with Caverns and Creatures, or organized however you want. For that matter, you can easily enough just use Caverns and Creatures, even though it's 3rd Edition.
For more resources I say to look through the Dungeon Fantasy and similar tags for PDFs. Save copies of the preview PDFs they give you - these can sometimes include equipment or monster stats which you can use as the GM even if you don't have the fullest extent of the GURPS rules at your disposal due to being stingy or poor (like me). You can usually make fairly common sense judgements of what things do based on their names and prices, and even if you get it "wrong" by winging it there's nothing wrong with that. It's what most D&D Dungeon Masters did in the old days due to rules incompleteness so why should you let it get between your players and the monsters that are in the way of their loot?
Putting It Together
Personally I like to make a list of weapons and armors available, with their relevant stats, all in one file rather than having to pore between two or three separate PDFs. You might want to decide on what combat options you're going to use so you can decide what stats to not bother even charting up in the first place!
For less martial adventuring gear like poles, ropes, torches, and so on if you can't find any prices or weights for them in GURPS products, there are still free D&D resources which often list them in pounds for weight so you can use that if it's relevant. Prices you can try to convert with something like 1 cp = 1 $ or you can just wing it.
Making New Stuff
Okay, so for magic we've got the spells Lend Energy, Lend Vitality, Minor Healing, Ignite Fire, Shape Fire, Create Fire, Fireball, Light, Haste, Detect Magic, Shield, Daze, Foolishness, and Sleep. I keep forgetting how many they gave us! This is actually a pretty decent array of spells, and if you need more you just need to assign a spell name, describe its effects, give it a duration, and give it a cost.
Let's say the Light spell, which is only as bright as a candle, isn't enough for you. Well, let's make a more powerful version - one that can properly replace a torch and the caster doesn't need to Concentrate to move because the light sticks to an object.
Torchlight
The subject, or a fist-sized part of the subject, glows with the brightness of a burning torch for the duration of the spell.
Duration: 1 minute
Cost: 3 to cast, 2 to maintain.
It might not be exactly the same value as the officially designed spells advanced from Light in GURPS Magic, but it's there now and it can be used. You can do this for any utility spell - combat spells are the only ones that are tricky to price and even so here's a good rule of thumb:
Buff and debuff effects have costs scaled to how big an effect the caster wants, up to +5/-5, and usually only cost 1 or 2 FP per level to cast and either equal or half cost to maintain. +5 ST for damage? 5 FP to cast, 5 to maintain. +5 to DR? 10 to cast, 5 to maintain.
Duration is usually 1 minute.
Minimum level of Magical Aptitude is arbitrary, just assign it based on whether everyday wizards can do it, serious wizards can do it, or if it is a secret locked to only the most talented archmages. These are Magery 1, Magery 2, and Magery 3.
Here is the Map!
Who needs full tactical combat rules? Yes, mapping out a dungeon and using miniatures helps reduce confusion and a lot of the best parts of GURPS are things like its many intricate ways of handling tactical combat with movement rules and the like. If you aren't going to just use Basic Combat, here are some expansions to make that will still keep things simple:
All melee weapons and unarmed attacks can only attack a foe in a space adjacent to the attacker. Doesn't matter that a fist doesn't reach a full yard or that a spear might be two or three long, just don't worry about reach.
Range is also ignored. In the dungeon it's so tightly packed with small rooms that throwing weapons aren't going to reach their maximum range, so why bother tracking it? Just assign a -2 to the attack roll if the foe is more than five spaces away and an additional -2 for each ally in the way that you don't want to hit. Ranged weapons have poor damage and hit chance in exchange for keeping you out of melee range.
Nothing grapples. Nobody grapples. There are no grappling skills in GURPS Lite so just don't worry about grappling.
There you go, a quick and dirty dungeon you can stock with monsters, traps, and treasure! I hope someone likes it.
It's a Trap
Statting up traps is deceptively simple. Just decide how it's noticed by PCs, how to disarm or avoid it, and what happens if it's triggered.
Giant Pendulum Blade
Detection: Automatic. You aren't going to miss that giant pendulum axe swinging back and forth across the hallway!
Disarm: Traps-10, 1 hour. This guy really knew what he was doing - it's better to go around it. On a critical success, the party now has a 25-lb Greataxe with -4 to hit on attacks and the trap is gone instead of just disabled.
Bad Stuff: Dodge the blade (+4 if not in the heat of combat) or take 3d cut damage.
Dart Shooter
Detection: Per-5 or Traps+1, whichever is greater. This is a classic trap and many a delver knows those pressure tiles on sight.
Disarm: Traps-1, 5 minutes. On a critical success, the party has a new crossbow (rated ST 14) rather than the trigger tile being merely disabled.
Bad Stuff: Dodge the crossbow bolt (-2 if distracted by being in combat when the trap is triggered) or take 1d+2 imp damage. If wounded, take 1d-3 toxic damage and roll HT-4. On failure, you will take 1 toxic damage per hour for the next 24 hours unless the poison is neutralized. You cannot be healed until the poison has run its course or been cured.
Made up completely on the fly, it's that easy!
Get Players And Play
This part I've never succeeded at, so best of luck to anyone interested!
