[PTTG]

Whoops. Should have called 'em hell parallels. Find and replace I guess.

These are all worlds which are terrible to visit and which have dying or no civilization, likely no humans. Fun places to vacation....

Global Cooling: Coal and oil reserves around the world are laden with a light, highly reflective aresol particulate that survives the burning process. Starting as early as the 1910s, a slight decrease in temperatures was detected; the response was to burn more fuel to keep warm. The spiral was terminal from the '40s, and in the present day of 2020, even clear days are noticeably dim in comparison, and temperatures are plunging. Civilization is collapsing in food riots...

Drexler: The discovery of a (local superscience) way to dispose of waste heat and manipulate atoms in 1999 lead to the production of grey goo nanomachines in 2012, which escaped the lab by November of that year. It took one machine 8 hours to duplicate itself; six broke containment into the soil, and so a little over a week later there was about 1 mole (the nanomachines being mostly carbon, that is almost exactly 12 grams) out of containment. Though math might say that earth would be consumed within a month, the surface is actually a pockmarked battlefield, some places intensely irradiated to destroy the sensitive nanites, other places doused in acid. No humans survive, as anyplace radioactive enough to resist the nanites is, well, radioactive. Fortunately for visitors, the nanites 'die' when not on their native worldline....

Strangelet 1 and 2: Strange matter struck Earth. Effectively a Vanish worldline. There's two of these; they actually can be detected by the characteristic, extremely brief signal response from the probes sent through.

Strangelet 3: Strange matter struck the moon in 1989. The pulse of radiation from the super-hot moon sterilized the Earth over a period of less than 24 hours, most of which were spent frantically traveling west to avoid the moonrise. Humans survived here for 45 days until the last vessels were lost.

Strangelet 4: (Not Hell yet) Mars was strangified in 1526. The nature of the transformation of the planet is a matter of intense theological debate. Visitors are concerned that Earth's proximity to the strangelet will eventually result in the timeline going the way of 1,2, and 3.

Beasts: In 1896, a team of archeologists opened a sealed stone structure in Canada, releasing tens of thousands of monsters, no two alike. The beasts were innate mana enhancers and mages as well, and today (1960), the only living humans are slaves for the beasts -- evidently kept solely for perverse entertainment. Most alarming, the structure was discovered directly underneath the location of Infinity headquarters.

Paranoia: Approximately 214 years ago, an unknown catastrophe afflicted the surface of earth, and since then, humanity has survived, barely, under the auspices of a friendly AI leader. Nothing can go wrong.