The Mega Dungeons Of The Petrified World For Your Old School Science Fantasy Campaign

Introduction : 

I've just gotten back this evening after running my players over my friend Larry's house through the mega-dungeons of  "The Incredible Petriefied World" . This one has everything I needed for a Crypts and Things hybrid game. The Incredible Petrified World is a 1958 public domain science fiction film directed by Jerry Warren and starring John Carradine. I used the idea of the characters following the first expedition in the diving bell into the no man's land of the inner caverns  of the "Petrified World". 

Plot Outline According To Wiki : 

Professor Millard Wyman’s (John Carradine) sends a crew of two men, Paul Whitmore (Allen Windsor) and Craig Randall (Robert Clarke), and two women Lauri Talbott (Sheila Noonan) and Dale Marshall (Phyllis Coates), down to ocean depths never before explored. But, there’s a technical problem during the launch and the mission is believed lost.

Miraculously the crew survives the mishap. However, they fear that their inevitable deaths are only postponed because they broke free of the cable connecting them to the surface and lost communication. Someone spots light out the bell’s window. They don’t understand it but they believe they moved up from where the mishap began. They determine that the pressure should be tolerable at a depth where light can be seen. They don their scuba gear and leave the bell. Instead of reaching the surface they surface in a cave. The crew explores the cave and finds a giant lizard. They also find a skeleton, then a living man tells the crew that he suffered a shipwreck fourteen years prior and found these caves after sinking into the ocean. He claims there is no way out and a volcano provides air to the caves.

Meanwhile, men working on the mission from the surface with sonar discover some unusual shapes moving near the doomed diving bell. Their bosses think it’s probably nothing. Prof. Wyman’s younger brother builds a bell but the launch is canceled. Prof. Wyman shows the man in charge of his brother’s mission modifications that he’s developed from the mistakes he made with the first bell. His pitch works and the second bell is launched. However, with the man in the cave becoming more suspicious and the volcano grows more unstable the second mission may not find them in time.

The Mission: 

The PC's were part of the the third expedition into the inner Earth caverns of the Petriefied world. They're to follow the route laid down by the other to expeditions and explore the region for possible mineral, natural resources, and unknown species.
The "Petrified world" is a vast no man's land between the outer world and the inner world of Pellucidar. The party used another modified diving bell to explore the inner realms this evening and barely scratched the surface of this vast inner realm.
The party consisted of six players : 

1. Jacob with a fifth level fighter/adventurer Captain John Hamen leader of the expedition 
2. Jennifer played Ruth Colby a tough as nails fourth level thief/reporter 
3. Jason played Dr.Issac Turner Occult expert and wizard seventh level
4. Steven played Hargo Johnson 5th level Barbarian and sailor 
5. Larry played Jason Thebult seventh level fighter, crack shot, and diver 
6. Cassey played Shifty Turner 7th level thief and diver 

The party dealt with any number of obstacles and many of the monsters in tonight's game were taken directly from the 1st edition AD&D Fiend Folio. The Folio provides and exceptional range of odd and alien monsters with a real inner world bend.
 The crew mostly made it out alive with the exceptions of Shifty and Ruth Colby. They met their end in the gullet of a Bone Snapper. The party dealt with a very nasty survivor/psychopath who led them into a trap after showing the party a cache of Atlantian artifacts that he had stumbled upon. The party of adventurers made it back to their own modified diving bell with biological specimens, several deposits of minerals, and a single Atlantian artifact straight out of the AD&D DM's Guide. 

Full Movie 

Using The Petrified World For Your OSR Games 

The Petrified World is a perfect bridge gap between your old school fantasy games and a modified modern game. The region acts as a sort of modern take on the "Underdark" of  Forgotten Realms fame. This region however acts as a catch all zone in my campaigns where the lost, damned, and castaways end up.
Here the DM is free to stick his favorite inner Earth plot hook without damaging any future campaign ideas he might have. Alien monsters, dinosaurs, and weird sea monster insects of unusual proportions work best.
The idea of what I like to refer to as "temporary ecosystems" can spring up for a time and then with the wave of a volcano disappear in a flash. Only to reappear on of a party's radar at a later date. Anything might be found within the zones of the Petrified World. From Japanese mutant dinosaurs, to entire extinct populations, to Lovecraftian hybrids and the limit is the DM's imagination.
The more alien the better the monsters seem to be for this style of game seems to suit the players.
For a game like Mutant Future "The Petrified World" is a perfect introduction point for a B monster movie invasion of the post apocalypse landscape. For Labyrinth Lord the inner world zones offers isolated pockets of fantasy adventure worlds of smaller and more intimate scope for modern characters. With Carcosa this style of game can offer a smaller slice of the Lovecraftian madness in a modern setting. A lab of the Snakemen might be found below ground and Atlantian artifacts generated using the Carcosa system. 

 Who knows what horrors await my players the next time they visit the Incredible Petrified World!