Random Adventure Generator

ThemeEspionage
Espionage adventures are active, grim scenarios involving spying and perhaps other cloak-and-dagger deeds such as assassination or rescue.
GoalSettle a Debt
A player character may find himself in the position of needing to settle a debt. He could gamble away all his money and need to raise some more to repay the gambling house before its enforcers come for him. On a more personal level, the character may need to settle a debt of either money or honor that he owes to an NPC.
Story HookBetter Late than Never
Some bad guys have arrived and done some bad guy things. The PCs were none the wiser. The bad guys have now made good their escape, and the PCs have caught wind of it in time to chase them down before they make it back to their lair, their home nation, behind enemy lines, etc.
PlotGeographic Progression
This is the simplest sort of adventure plot. The heroes have an area to investigate or travel through; they have encounters based on where they are. For instance, the traditional dungeon, where monsters are tied to specific rooms or areas. Or, if the heroes are travelling along a narrow valley or through an enchanted forest, they might suffer ambushes and other encounters fixed to various points along their travel plan. The plot, then, is getting to the villain by surviving the intervening obstacle encounters.
ClimaxChase to Ground
First, you have the Heroes Chasing the Villain. The villain, after a series of encounters with the heroes, is running to safety, to some place where he can acquire more power, or to somehwere he can accomplish some dread purpose such as assassination or mass murder. The heroes chase him, have to deal with the obstacles he leaves behind, and finally catch up to him before or just as he reaches his goal. Here, we have the final duel between the villains forces and the heroes. Second, you have the Villain Chasing the Heroes. Often, in a story like this, the heroes have found out how to defeat the villain -- such as getting to a particular temple and conducting a particular ritual. The villain chases them all through their quest, catching up to them just as they're commenciing their ritual; they must, with heroic effort, conclude the ritual while suffering his attacks. Third, you have the Master Villain's Sudden Escape Attempt. This takes place in adventures where the Master Villain's identity is unknown until the end. His identity is revealed and he makes a sudden bolt for freedom; the heroes give chase. This usually results in a dangerous foot-chase through nasty terrain -- such as across rooftops, through the dungeons, or across an active battlefield.
General SettingTorturous Terrain
The adventure takes place in some sort of unsettled, uncivilized, dangerous terrain; in action stories, the desert and jungle work best; choose one of those two or decide on a setting that is similarly dangerous and exotic.
Specific Setting ILost City
This is the remnant of some lost civilization or expedition, still thriving in some forgotten corner of the world. Remnants of lost civilizations can even inhabit cavern systems beneath campaign cities, preying on the above-worlders for their goods, slaves, and sacrifices.
Specific Setting IITavern/Inn
This is a classic fantasy setting, the residence of travelling heroes and the home of the tavern brawl.
Master VillainOrganizer
This Master Villain is the head of the local criminal syndicate -- the Thieve's Guild or slaver ring, for instance. He's cold-hearted and unsympathetic, and human life means nothing to him. He employs assassins and musclemen against the heroes, and can only be reasoned with when it's going to profit him more to cooperate with the heroes than kill them.
Minor Villain IChildhood Friend with a Dark Secret
This Minor Villain is like the character of the same name from the Allies and Neutrals section. However, the heroes find out early on that he's really working for the Master Villain. He may not wish to be helping the villains; his family may be held hostage, or he may just be too frightened of the villain or otherwise weak-willed to refuse. Alternatively, he could actually be evil now.
Minor Villain IIChildhood Friend with a Dark Secret
This Minor Villain is like the character of the same name from the Allies and Neutrals section. However, the heroes find out early on that he's really working for the Master Villain. He may not wish to be helping the villains; his family may be held hostage, or he may just be too frightened of the villain or otherwise weak-willed to refuse. Alternatively, he could actually be evil now.
Ally/NeutralMerry Minstrel
This character follows the heroes in order that he might find inspiration for his song and storytelling. He can't be shut up; he sings all the day long and into the night, is a showoff before crowds, and is far too noisy for a party trying to remain unobserved.
Monster EncounterBeast Amok
Some time when the heroes are in a village or city, an animal, probably an otherwise tame or captured beast, is set loose by the villain's minions or driven mad by the Master Villain. The beast goes berserk in the crowds; if the heroes aren't inclined to capture or kill it, it goes after them.
Character EncounterNew Enemy
In the course of his ordinary activies, one of the heroes can make a New Enemy. Hurrying along the street, he can bump into a disagreeable fighter for whom an apology isn't enough; in a tavern, he can make some innocuous remark that you deliberately have the irritable fellow misconstrue as an insult. The New Enemy will only exchange heated words with the hero at this point, but will appear again later in the adventure and will eventually have to fight the hero.
DeathtrapColiseum
If it's appropriate, you can have the heroes captured by the local authorities -- particularly when they're in an exotic land, lost world, or whatever -- and have them armed with gladiatorial gear and dropped into a coliseum for the entertainment of the locals. (Note that this works much better with fighting-type heroes than spellcasters.)
ChaseAerial
The heroes could be riding pegasi or friendly griffons or allied great eagles; the villains could be carried aloft by gargoyles or demons. The prospect of taking a mile-long fall if one's mount is hit is a very daunting and challenging one for the hero.
Omen/ProphesyReincarnation
The hero, seeing the portrait of some long-dead nobleman, may be surprised to see his own face staring back at him. All evidence points to the fact that our hero is the reincarnation of this person, and the Master Villain may desire to destroy any trace of that nobleman's existence. Just as appropriately, this long-dead nobleman may have died after making some important choice -- such as choosing love over career or career over friends; and the choice he faced is identical to the one the hero now faces. Will our hero defy the prophecy and choose as he did in a previous life, or will he choose the other option and see what happens?
Secret WeaknessElement
The Master Villain can be banished, dispelled, killed, or otherwise defeated by some of element or item. The Master Villain tries to get rid of all the examples of this element in his vicinity; he doesn't let his minions carry it or bring it into his presence. But he's not stupid; he doesn't announce to the world what his weakness is. He tries to hide his concern within another command. If he's allergic to red roses, for instance, he orders all "things of beauty" destroyed within miles of his abode.
Special ConditionTime Limit
Finally, the most obvious condition to place on an adventure is to give it a time limit. If the Master Villain is going to conclude his evil spell in only three days, and his citadel is three hard days' riding away, then the heroes are going to be on the go all throughout the adventure -- with little time to rest, plan, gather allies, or anything except get to where they're going.
Moral QuandrySaving Quandry
Finally, another classic quandry puts the heroes in the position of choosing between a grand opportunity to hurt the Master Villain -- or saving the lives of a number of individuals.
Red HerringArtifact that Doesn't Work
Often, epic quests against powerful Master Villains require that the heroes find some legendary artifact, the only object which can defeat the villain. If your heroes have had no trouble getting to the artifact -- they've effortlessly sliced through every obstacle you've put in their path and are confidently advancing on the resting place of the magical item -- you can have it not work.
Cruel TrickWanted by the Law
One final complication, one which occurs pretty frequently, is when the heroes are wanted by the law. When they're wanted by the law, they have to travel in secret and very limited in the resources they can acquire.

Based upon tables from the Dungeon Master's Design Kit by TSR, Inc.