Famously, AD&D had a dungeon generator for its first appendix, allowing you to painstakingly roll up a dungeon corridor by corridor. I have adapted it to automatic generation here, so you can allow the oracular spirit of Gary Gygax to guide your hand without consulting sub-table after sub-table. Several abrogations have been made for my sanity.
Select a direction and hit the "Periodic Check" button. If you encounter treasure, at your discretion you may press the "Container Defense" button to see how it is defended. The third and fourth buttons are not from the original Appendix A in any way, but I thought it would be appropriate to supplement with the standard empty room list and some generic monsters, if you don't have an appropriate list at hand. You will have to come up with your own magic items if any are rolled.
Adventurers have a romantic view of magi. They are not the usual targets of arcane predation-- they have no children to steal, and if the head of state is impersonated by a wandering sorcerer, that's only good for business. Some were even raised by those magic-seeking freaks.
The problem is that all the best spells of slander and double-dealing are easy to acquire if you are a total cad. A wizard is a con artist who has demonstrated their willingness to break seals, read aloud from unknown tomes, and release bound evils. They must be kept from artifacts of power as a matter of simple civilization.
This class works to make PCs without having to roll on a spell list. For powerful NPC wizards, you can just pick up a class like this and roll several magic tools of folklore, or allocate them powers as appropriate.
Start with: a long beard, a long hat, a long life, one inventory slot's worth of pure muscle, and a magic tool of folklore.
A: Ripped, Spells
C: Curse Reversed
Ripped: You can fill up to [level] inventory slots with pure muscle. For each slot filled, you get +2 to most tests of strength (but not attack rolls), and your kung fu deals +1 damage. A week of slovenly living degrades a slot of muscle and a week of shadow-boxing adds a slot of muscle.
Spells: Against foes of equal or lesser power, you may disguise yourself and see through their disguises, tell extremely convincing lies and easily discern their lies, conceal your intentions and know their intentions, make objects appear valuable or worthless, and make ordinary random events go your way.
Against foes of greater power, things are more complicated. You can increase the odds of successfully working a spell (from 0%) by 20% for each of the following conditions met:
You know their true name!
They have cheated or wronged you!
You have put a curséd totém in the place where they sleep!
You have put something from their body (hair, blood, etc.) into a curséd doll!
The gods themselves cry out for their destruction!
Signs: Spend an hour in communion with the energy of the world to receive a confusing vision of a topic or question of your choice. This grants at least three significant images, tableus, names, or actions.
Curse Reversed: when you encounter ongoing magics, you intuitively understand a method to undo them. It may not be easy but it is always effective.
Domain: you start to attract the service of strange beings. Every time you seek hirelings, you find an equal number of monsters and extraplanar beings to swell your ranks. When in your home (or home complex), you can project a hologram of your head throughout its extent, seeing and speaking through it.
BONEPUNK is a beautifully-formatted game in which you play the undead who are exploited in an industrial necromantic society. It is awesome in the "play a giant gorilla skeleton" way while still being tragic in a "sell your bone marrow" way. It is free here.
G20 is only three pages long but it forms a flexible basis for many games. If you have four-level classes you want to use, and you want to play in ten minutes, this is a good way to do that. It is free here.
The GROG combines light rules with the tactical combat of 3rd edition D&D, allowing for satisfying combat play without sacrificing finesse-in-play at the table. It is free here.
HEIMJING is a D&D-like game with a built-in setting that totally changes the way the game works (gravity is reversed for humans), even when you're just going into and out of a dungeon. Its zodiac mysteries offer an intriguing personal quest for player without disrupting whatever game the DM is running. It is free here.
MARROW is a light, experimental classless system, where the weight of the system is in the management of different sorts of inventories not only for your belongings but also your skills, spells, languages, and more. Sort of like KNAVE to the max. It is free here.
Runaway Princesses is a game made to be accessible to people who primarily have experience with the modern edition of D&D. It takes time to define its terms and give advice, all in a well-formatted document. It's not the shortest or lightest rulebook, but it can be familiar to people trying to branch out. It is free here.
Vain the Sword is a mythic-folkloric fantasy game, a simplified hack of D&D-esque dungeon system. The rule set offers a tragically heroic skew on classic old-school problem-solving play, with stunning original art. It is free here.
There are plenty of other great games I could go into here, but the sheer number of free dungeon games online is an embarrassment of riches. If you seek more games, or inspiration for the great games you will write, please feel free to contact one of the community's servers here.
This small dungeon-space is at-home almost everywhere. I put it on an abandoned island in Acmori. The inhabitants of the nearby island claim a wizard lives within the impressive stone tower against the mountain, but he has not been seen for years.
The tower is crudely fashioned of dark bluish stone, its plaster eaten more and more each year by moss. It is a near-unthinkable seven stories tall, leaning slightly forward. Its windows are but thin slits, save for a balcony on the front of the fourth floor. Each floor is about thirteen feet high, and the tower has a diameter of forty feet. Unless otherwise stated, assume the thin window provide dim light during the day.
Support beams along the walls are rotted and marred by graffiti. The floor has fallen away in places, revealing a loose and debased foundation. On the far side, the stairs run along the wall.
The stairs continuing on the third floor are barricaded with boards, branches, and nails. This floor is mostly empty save for a straw mattress, broken desk, and a pair of dull knives. Two small chutes in the ceiling hang over small piles of ash.
From the oxidation of the nails, it is clear the barricade was made over a year ago. It is easy enough to deconstruct from this side, though disturbing it causes vertigo as the room shakes slightly.
The stairs continue on to the fourth floor. This room is a forge, but attention is drawn immediately to the large alabaster idol against the opposite wall. It is graven to represent a woman engulfed in flames painted many colors. In her left hand she holds out a lump of polished black stone. The rest of the room is full of poorly-forged blades in various styles and states of completion.
This idol is of a goddess obscure in this part of the world, one of fire, radiation, and the ephemeral. The lump of stone is ebony carved into the shape of a hand and polished, gives DR 3 against radiation, and is worth 35 gold coins even to those who don't even know its true significance. The idol itself is worth much more, but any attempt to move it will cause the tower to shake and possibly collapse.
The swords are variously dented, impure, brittle, or poorly-balanced. One, a silver xiphos, is worth a couple gold coins due to its material value, but otherwise they are not valuable.
The stairway terminates here with a wall screening someone ascending from the rest of the room. To the left is the balcony. To the right is a cage with a shining bird. To the far wall is a stairwell ascending. Anyone who reaches this floor notices (especially if they have no other light) a strange glow of shifting color coming from the room beyond. This comes from a creature I will here call an atomic phoenix in the cage.
The light of the phoenix is harmful, dealing HP damage based on the amount of exposure. Peeking around the corner once hurts but doesn't take points off your total. Running across the room to the far staircase inflicts 1d6 (assuming the average character has like 8 hp.) Running towards the cage and unlatching it does like 3d6. Overturning a table and dragging it around as a shield does 1d4 or possibly no damage, depending. If the bird is unlatched it will immediately fly out of the balcony. It is intelligent, of equivalent rank to an angel, and speaks bird language as well as any legal speech.
The room is full of various furnishings-- tables, desks, crates, and the like, all left here for storage. Searching them yields nothing but a dead family of mice. Moving one around without counterbalancing the weight causes the tower to shake. Moving more than a couple risks toppling the tower.
On the balcony is a suit of straps and plates of lead. Acts as heavy medium armor, and makes someone mostly immune to radiation from sources they are facing.
Anyone who steps fully onto the balcony will cause 1d4 sparrows to fly up to them. If they speak bird language, the sparrows will explain that the wizard used to give them errands, but they haven't seen him for a long time.
The stairway continues to the sixth floor. This floor is a lounge. Comfortable stone couch. Out-of-tune harp. A cosmetics table with an impressively wide bronze mirror. The weight of more than one person here can cause the tower to shake if not carefully counterbalanced. Egregious distributions of weight cause the tower to collapse.
Most of the cosmetics are dried out, but a couple still preserve. There is eye shadow that replaces your color vision with heat vision for as long as you wear it. Also fun weird wizard make-up as improvised.
The stairway shakes as you climb up. It continues to the seventh floor. This room is filled with rows of scroll racks. Further within, a corpse in dark green robes decompose, staring in your direction with impeccably shadowed eyes.
This is the corpse of the wizard. Lying open on his chest is his spellbook, containing the spells Form of the Dragon, Illusion, Sympathy, Forbidden Snakes, Magic Counter, Bite Augury, and Speak with the Dead.
Searching the rest of the library reveals the following significant tomes (consult your secret library handout): Blood and Glory, Eternal, The Lies of Domesus, and Torture In The Land of Makhazin. The rest are travelogues, bestiaries, rumors of treasure, local histories, and commentaries in the following languages: Acmor, Nasjicu, Trepaniet, Bird.
The stairs end here. It is clear the tower is swaying. The room is empty save for a mosaic of concentric circles in the floor and a golden orb set in the ceiling.
This orb is about a yard [~1 meter] across, of intricate golden filigree. It has a wide button in the very bottom. The hemisphere it is built into is a little wider than it, and the edges seem to bump against the orb.
If someone presses the button in the bottom of the orb, it will fall to the floor. Lacking its main support, the tower will pitch forward and fall. This kills the occupants. If someone presses the button again, it will hang immovably in space. If this is done to arrest the tower's fall, most of the top floor will hang off the orb, but the rest of the tower will fall to the ground.