Reality starts with three immensely long tunnels. The three tunnels are clearly artificial. Nobody knows who originally constructed them. Nobody knows how far the tunnels extend.
Each tunnel extends for at least tens of thousands of miles -- maybe forever. Each tunnel is about fifteen feet wide and twenty-five feet tall. The tunnel walls are some kind of indestructible white material. Light somehow shines down from the ceiling.
Each of the tunnels in These Strange Worlds contains thousands or possibly millions of Doors. No two doors are exactly alike in size or appearance. In many cases, the character of the Door gives some hint concerning the reality beyond. In a few cases, there appears to be no connection between the Door and the reality at all. The Doors are usually about twenty feet apart and never more than a hundred feet apart.
The three tunnels are designated Red, Blue, and Yellow.
Strange World Blue doors allow a form of time travel and provide access to future worlds. Complex and sometimes poorly understood natural laws control and in most cases prevent paradoxical changes in the time stream. It isn't generally possible to visit one door, read the paper, and then go to a door to an earlier era and buy a winning lottery ticket. In fact, you might not even remember reading that future paper in the first place.
Strange World Yellow allows another form of time travel, but only to "the past." In this case, every door opens into a different new reality. Very soon after each contact, events in the world began to diverge. It was sometimes possible to buy that winning lottery ticket. Or rediscover a gold field or contract with Mark Twain when he was 16. There are Yellow worlds where the Egyptian Empire flourished and Pharaohs maintain American colonies. There are also worlds where Neanderthals never became extinct and worlds where the American Civil War was fought with lasers and nuclear zeppelins.
Strange World Red is easier to understand in some ways and harder to understand in others. There is no time travel. Each door opens to a different location. And what locations! In Red, magic is possible. Humans rule, but only barely. Hundreds of different sentient races live in Red, including many whose whole metabolism is based on magic and not biochemistry.
New doors can be created if you have the right equipment. Doors can be opened, and one can observe what is behind the door. If one had different right equipment, one could then walk through the door and into the different reality. Yet more special equipment allowed one to come back.
If you travel one direction, each tunnel will eventually intersect at the infamous Nexus City. At the end of each tunnel is a very special door. These doors are much larger than usual and never lock or block passage. They each open into Nexus City proper, a genuine city that exists under a triangular dome. The architecture was as varied as the inhabitants. A skyscraper rises next to a rough hewn castle, both facing a park full of fountains and trees. A factory can be connected directly to an immense tree house complex and what could only be a train station. There aren't very many streets -- the buildings are just plopped down at random.
If you travel in the other direction, you could be in for a long trip. The first hundred or so miles extending out in three directions from Nexus City are relatively well explored. They continue many thousands of miles beyond this. Some hypothesize that they extend forever.
It's hard to explore great distances in the tunnels. Consider that there is no food, water or fuel unless you enter one of the plentiful doors. Radios, message lasers, and other communication devices don't work. Sound carries less than a mile. Although always brightly lit, It's even hard to see down a tunnel for more than half a mile or so.
Internal combustion engines work in the tunnels, but are frowned upon. There's some kind of monster who generally goes by 'The Boogey Man' who has been known to catch and devour cars, trucks, and motorcycles that venture into the tunnels. Then there is the problem of refueling.
Of course, just because it's hard doesn't mean it's impossible. The longest recorded roundtrip journey was a seven-thousand mile expedition down the Yellow tunnel in a specially designed electric trolley. The trip took about thirty days at an average speed of 25 miles an hour. The trolley used a thorium nuclear battery with a continuous duty cycle of about half a year. The explorers reported that even seven thousand miles down the tunnel, things were pretty much the same. The trolley was moved to the Red Tunnel, left, and never came back.
A Unique with the street name of Blaze-Laz Man could convert his body and personal equipment into coherent light. He'd been very successful transporting messages and equipment across the solar system at very close to the speed of light. With much fanfare, he announced plans to explore the first million miles of the Blue tunnel. On the appointed day, he checked his gear, activated his camera, and converted into an intelligent laser beam and went precisely nowhere. Apparently whatever prevented radios from working also prevented Blaze-Laz from traveling in the tunnels.
Magic has also been used to try to explore the tunnels. Teleportation spells are useless. Flight, Quick, and Endure spells allowed for the exploration of the Red Tunnel for several hundred miles. A Zombie Master envisioned a brute force approach. He created a thousand magically animated, deathless zombies and had them start walking down the tunnel. Every week, one zombie would pop a door, see what was inside, and start trudging back to report. The army could travel about 300 miles a week (no need to stop for food, water, or sleep). As predicted, they found that the further away from Nexus City, the more distant the land. After twenty weeks, the Zombies started reporting doors that mainly opened into North and South Atlantis. Then they stopped reporting altogether.
Attempts to explore the tunnels will no doubt always take place. There have been several hundred attempts to explore the tunnels beyond the one thousand mile mark. Why not more? Only a handful has succeeded. It is also important to remember that every mile of tunnel contains between one hundred and two hundred doors. There is no shortage of exciting places to visit without nearly the effort.
The following illustration shows the general layout of the Strange Worlds, including Nexus City. The home realities for some of the "31st Phase of Doors" Zone Pioneers featured in the novels are indicated (including their tracking number and home realities).
Doors in Yellow are typically named using three indicators: The year when discovered, the location of that reality's first door, and the number of years since discovery. For instance, "1881 Wupatki 16" means that a door first opened into the Wupatki Indian settlement when the year was 1881. This reality was first entered from the tunnels sixteen years ago and the current year there is therefore 1897.
Doors in Red usually just indicate the location.Doors in Blue indicate both the location and the current year.