This was used in a campaign in my custom system/setting combo. Pardon the length.
The town for Forest Grove is having a bit of a pest problem. For a number of years, they've had to deal with a strange variety of "rodent of unusual size". The things are harmless, but are damn frustrating. They have a drive to eat or take anything that is shiny or remotely edible. The town until recently kept them under control by culling the herd whenever the critters needed to be reminded to fear humans. Unfortunately, there's been a change of as late. It seems something else is lurking in the woods now after a particular large culling of the heard. The townsfolk are at a lost to explain this development, but they believe the critters originate from an abandoned facility deep within the woods.
When the party enters in the main strip of the town, they are immediately greeted by what seems to be squirrel like creatures the size of German Shepherds. They will approach and start sniffing to inspect each of the party members for anything edible (anything in a sealed container will not invoke a strong response, but anything opened or particularly odorous will get their attention). If they detect anything edible, the critters will try to get it in a docile manner, somewhat endearing to certain party members. If denied too long, they'll get VERY insistent and will eventually resort to using their sharp teeth to cut and chew through clothing and containers to get to the food. Weaker party members can get knocked down and swarmed by the critters. In a swarming, the critters will grab food and anything shiny. They'll leave party members relatively unharmed, but clothing and equipment can be damaged.
If the party tries to attack the critters, the townsfolk will plead for them not to kill any of them and just scare them off. If party kills a few, the townsfolk will not exactly be mad at them, but will seem more wary of what killing the critters will bring.
If the party asks anything about the critters, they get some more common information about the town and the critters. Most will not have any reliable information about the monster in the woods or the abandoned facility. Many will redirect the party to a local diner where they should find Milo and Greg.
At the Diner:
The diner is the local hangout with most the locals rambling about the same recent news. The only thing that sticks is two men near the front window. They are sitting at a table, with various books, notes, and scouting equipment on it. The entire tabletop is covered and overflowing with an geographic survey map of the area. The two seems to be debating about which routes to "the facility" they should attempt next time.
Upon investigation, the two men are Milo and Greg. Milo is a meeker man dressed in a more formal clothes and duster, he's the local self-proclaimed scientist. Greg is a larger, bulker one wearing a combination of old security gear and an old para-military contractor uniform. Milo has a slight warped Russian accent and Greg has a bit of twang in his voice.
When the party talks to them, they explain the situation in greater detail and give a list of observations:
There's never more than 256 of them, ever, including the monster lurking around.
If one is killed or dies, another one that looks exactly like will appear at least a day later.
When the lurking monster was discovered, one of the 256 critters hasn't been seen since.
The critters are sterile.
It's been mentioned in a few texts as a research facility.
It still has a few active defenses by the means of mast mounted plasma cannons.
Milo and Greg has forged a route that bypasses all the defenses except two.
Both men believe the answers for the critters and the current situation lies within the facility.
The party has a choice. They can either try the main route that leads up to the facility and attempt to brute force through a bunch of cranky plasma cannon turret towers, take the route Milo and Greg provide, or try to find their own route. Run and gunners might find it worthwhile to take the quicker front entrance. Parties who chatted up the Diner Duo, will be able to get a copy of the route the duo were working on. This requires convincing them that letting the party help is a good idea. Parties with exceptional skills in sneaking, scouting, trailblazing, or path-finding might find creating their own route to be successful enough to bypass all the security turrets.
If perceptive, the party will notice the towers slowly pan to scan the area... it is not particularly quick and there's a limited viewing angle for the sensors brought on by advanced disrepair. Whenever a turret detects something, it'll broadcast, on a loudspeaker, some garbled warning message. It seems the language setting on the text-to-speech system for the message system is on the fritz and will rotate between a few different languages... mid sentence. Parties with linguists or similar will be able to make out the "This is a restricted area. Immediately turn around and vacate the area or halt for security personnel." (FYI, there are no security personnel left.) If the warning isn't heeded after three broadcasts, the turrets will open fire on the target. The targeting system isn't very advanced. It only identifies moving objects. It will target and lock onto the first one it sees. If it starts firing on the target, it will attack that target until there is no further movement.
If the party took the route suggested by Milo and Greg, they get to a guarded clearing with a tower ontop of a hill. They'll be near a rocky outcrop that is sheltered from view of the turrets, with plenty of rocks for the party to test their theories about how the turrets target and work. If they are exceptionally athletic, lucky, and have good timing, a party member can rush the hill out of view of the sensors and charge it before the turret pans to scan back. The turrets, by design, cannot fire below a certain arc. So any party members underneath the turret are safe to do what they want to tackle the tower.
The second tower is barely working and isn't much of challenge. It'll actually overload and it's generator shutdown after firing once.
Into the Facility:
The facility looks small and lackluster. It is only one tall story high and modest in width and length. The main area outside is a large parking lot with large exterior doors opening inside to a sheltered parking area inside the facility building. If the party lingers too long in the area, they may catch a glimpse of the lurking monster, who will run off at the first sign of being spotted.
Inside there are two elevators. One is still functional, the other no so much. In the broken elevator, there is no elevator car visible, the elevator doors are thrown open, and there is mud, debris, and other refuse surrounding the area. There are signs of large claw marks on every surface of the exposed elevator shaft.
Reception, business, and living quarters. The area is fairly mundane. The are a few scattered historical items and a few interesting bits. The one item that stands out is the lounge. There is an audio recorder still functional and it has a variety of audio logs from the Head Security officer. It starts out detailing the events of the apocalypse from his perspective. Strange things, odd occurrences, and the eventual abandonment of the facility. Occasionally, there is a another voice with a strong Russian accent in the background to go along with the twangy southern voice. The last message is of him stating all the access codes, and giving what knowledge he does know of the layout of the facility. "No sense in locking up if you don't plan on coming back." He mentions that only he and another researcher have stayed the few weeks to wait out the worst of the nuclear bombardment. He figures he'll head out with the researcher to the town nearby, since they'll be a lot more useful out there then cooped up in here.
Biological Research. A party member skilled in medicine or cybernetics may find some useful items about. There are a number of stored experiments, many of which having survived storage due to systems failure. (There is a bit more, but my setting has genetically engineered creature making their own civilizations. In the version that was ran, the is a male and female precursor to one of the newer species in the world safely in cryo storage.)
Weapons Research. Many of the good weapons were taken, but there plenty of parts and pieces to be found. And there are a number of nearly finished pre-fall guns about. Unfortunately, there are a number of completed flawed weapons in the mix. Good hunting.
Collapsed. The majority of the floor is collapsed in on itself and very little is accessible. There are a few stable explosives and other munitions around. Geiger counters will pick up higher than normal readings in this area.
Getting to this floor takes a while. There is a VERY long timing gap between the 4th and 5th floor. Upon exiting the elevator, the party is hit with a horrific smell that permeates the air. The odorous funk adheres itself to the party's clothing, it is so fowl. The elevator lobby is a dirt, shit, and trash strewn sty that'd make a pig puke. The doors to the broken elevator shaft's doors are wide open, with noted huge claw marks everywhere.
As the party enters deeper, they come across rooms with computer systems active, but in failing states of disrepair. Errors erupt onto screens before the system restarts itself and repeats the pattern. The final observation area has the most functional computers and a grant view to a strange sight. In a cavernous area, a massive collection of biotech machinery and automated robotics churns loudly. Moving bio-storage tank from one rack to the next, draining and filling fluids, and eventually placing a sole container overhead into a chamber. With a grand display of alarms, steam, flashing lights, and a eruption of synthetic amniotic fluids... A critter is flushed out onto the "factory" floor.
The computers update their statuses. The screens show ID numbers: 0 - 255 All have various statuses: Living, Dying, Dead, Growing, and Incubating. There are two unique statuses. 255 has the status of "Released". 0 has the status of "ERROR".
The "ERROR" becomes blatantly obvious as a monstrous form pounces from the shadows onto "255". In a brief few moments, "255" is shredded by the monster as it gorges itself in a very fresh meal. The status of "255" changes to "Dead." If the party is quiet enough (lots of loud machinery) they can leave without disturbing the monster. Considering the monster is roughly the size of a VW Bug and has the temper of a wolverine on PCP... it would be wise for a party with less combat prowess to find another way. Otherwise, the party will have a horrific fight that could cost them their lives.
Party members with excellent computer skills can figure out a way to override the erred system and halt the production process. Those with medical knowledge, genetics, engineering, and other relevant skills have a chance of discovering information about the "biological failsafe" for experiments gone bad and where it is kept (2nd floor).
Facilities. The floor isn't as elaborate as the rest. There are a few control rooms in an observation deck over the various power junctions, air exchanges, and plumbing systems. There are many things that can be done in this area. The power generators can be shutdown or sabotaged. The air circulation system can be shutdown. The water can be turned off. Or simply, the party can cut power from certain floors. (The 5th floor, in particular, is eating a lot of it.)
If the party explores the base, deals with beast (either by killing it, trapping it, or activating the failsafe), and stops the production: The town is very pleased! If the party reveals the good news in the diner to Milo and Greg, the diner clears out as the locals proceed to remove their town of the critters and scare them off for good.
If the party explores the base and deals with the best: They'll be quite appreciative to finally know what the hell is going on. Later, the town reports they setup a group inside the facility and eventually got the production stopped.
If the party explores the base and stops the production: The town will be happy, but very wary since the lurking beast is still around. Later, the town reports that the beast eventually ran out of food and attacked the town. It was slain after a fight and many casualties.
If the party explores the base, informs Milo and Greg, and then ditch: The town can't exactly blame the party and still thanks them for forging a path into the facility. They expect it to be a difficult chore, but they figure out how to put a stop to all the problems running about.