Areas of dimensional instability first started to appear in the time of the Ancient Ones with the 'The Amazing Stranger from Another World Affair'. A space craft appeared in the skies in 1918 to the fanfare of the world at the edges of the outer solar system through a rip in the fabric of time & space. Scientists, physicists,astronomers were able to chart the very bounds of reality. The adventure career of the occupant of that craft is well documented elsewhere & far to much for a single blog entry. Needless to say that this single event catapulted the world's sciences decades forward on all levels including FTL travel,astronomy, physics, even the basic building blocks of what we call reality.
The second event is 'the mysterious Warden event' in which an interstellar traveler from a far away world crashed into Earth in 1922 in the then Yugoslavian mountains. The disaster devastated local villages, cities, & burnt massive swaths of the countryside. The loss of life totaled in the thousands but then the monsters started to appear. A few at first & then more. Teams of international scientists, explorers, etc. were sent in & none returned. The reports of monsters continued, a few artifacts of incredible technological potential were recovered. During World War II the Nazi conquered, sent in teams, & died by the hundreds.
The Americans & Soviets sent in teams as well learning from what they could about the craft.
A few baubles were recovered which propelled the sciences once again this time in medicine & energy production. The biggest break came in the early Fifties after the 'California They' disasters which were indirectly influenced by the mutagen forces released into Earth's atmosphere from the craft. Scientists incorrectly attributed it to the atomic bombs. An engineering bot was recovered after repairs on the crashed craft were being done. A mercenary group managed to smuggle the bot out of the restricted area. The bots data banks took decades to decode by the R.U.R. think tank. This lead to a revolution in robotics, A.I., & the fields of artificial intelligence that is barely understood. The appearance of the Warden on Earth signaled a barely recognized start of events that spelled the end of Earth. The Hyperborean & Mound wars started a few short decades later. The end was on its way.
Bubbles of dimensional unreality lead to other dimensions & alternative Earths making the whole place one of the most dangerous on Earth. Adventurers, scientists, and dimensional trespassers routinely come through this place. To this day not many have penetrated the secrets of the Warden. It still stands quietly being repaired, worked on & tinkered with by its robotic & monstrous inhabitants.
So what is this above? A brief set of passages based on my 'Old Earth' campaign history's time line. What I've done is basically taken a classic TSR era module & molded it around the needs of my players & the campaign setting's history.
There's a quick background, some fun fluff, & a way of combining this with any number of retroclone systems.
"S3: "Expedition to the Barrier Peaks" (1980), by Gary Gygax, is the third "Special" adventure for AD&D. It was published in February 1980.", is one of the more flexible & completely adaptable but very deadly adventures. I've used it numerous time for weird fiction ala James Raggi IV's Lamentations of the Flame Princess, Rpg Pundit's Dark Albion, Adventurer, Conqueror, King, & even Stars Without Number. The point is that one module can be used to set up & run an entire campaign setting as its touchstone. Hell,
The Grand Duchy of Geoff could become a pre WWII micro nation that hires the adventurers to penetrate & possibly die among the mysteries of the Warden. Dungeon masters should never ever be intimidated by 'classic' adventures because other gamers have strong opinions about these classics. Your players are the one who matter and its them you are playing with.
May all of your saves happen & you roll twenties. More to come!