The Next Time the Adventurers Step Through a Portal ...

... maybe they step into this.

Roll - Destination
1 - Alien city (see above) during an important ritual. There is a 50% chance the visitors are welcomed as emissaries from the gods and imprisoned in a palace of alien pleasures (if only the PCs could digest the alien food) and a 50% chance they are treated as intruders and put to death by a thousand searing rays.
2 - Step into a cellar at the moment Aleister Crowley is summoning a demon; Crowley must pass a system shock test or suffer a heart attack. His patrons may not take kindly to the intrusion.
3 - Pass through an atomic feedback flux loop onto the starship Warden. Everyone must pass a saving throw (vs. poison) or suffer a mutation.
4 - Find themselves in a cluttered wardrobe that leads into wartime England. They are welcomed by a man in a natty suit (Merlin) and pressed into a mission to assassinate Adolf Hitler.
5 - Walk into the lowest level of Castle Greyhawk with no memories (though spellcasters retain their memorized or prepared spells) of how they got there.
6 - Step into a massive submerged cavern and the grand council of dolphins. A dolphin mage will work fast to summon up airy water.
7 - Awaken in a brilliant woodland on Midsummer Night; cavort with fey both good and evil.
8 - Find themselves on a barren world as the representatives of Law in a gladiatorial combat with their opposites from another universe as the representatives of Chaos.
9 - Enter a padded cell of Bedlam asylum, where they must save a mad woman from the machinations of Fraz-urb'luu, for she alone can open the portal back to their world.
10 - Step onto a solar barque making its way across the skies of a mythic earth, moments before it passes into Hades.

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Image (top) from Golden Age Comic Book Stories.