We just finished the Ghost of Thunder River adventure from Jeweled Thrones of the Earth. I had Thumocris open up a portal to ancient Acheron as part of the climactic battle (the PCs were basically untouched during the battle, that’s another topic), and a few PCs were sucked in.
Now I’m looking for an adventure that I can easily set in Acheron, along with a portal to get them back to “modern” time. Any suggestions?
I don’t really run pre-made adventures so I just cooked this up.
What if your players get transported in an area where the Hyborian tribes live. One of their shamans might know a way to send them back but he might want the player charater’s aid first.
Yeah, something like this sounds like a good setup. I was thinking of dropping them in the middle of something nasty - like a sacrificial feast of human flesh, and they need to get out… Next step might be to want to get back. Problem is, they might not want to 
Honestly I would drop them in unsettled wilderness, maybe a dark forest filled with dangerous animals.
After they get out they’d come across a violent Hyborian tribe which they would have to calm down. After they manage to defuse the situation they could talk with the shaman which knows a way to send them back but maybe needs them to get an item for him.
Maybe a magical item from an acheronian sorcerer. Which would mean they have to infiltrate an acheronian city somehow and steal that item from its current owner.
All of this would be better if they don’t know which time period they have transported to. They’d have to figure that out which is another layer of mystery.
Could be a good use for the kull of atlantis book?
I’m not familiar with that setting at all, isn’t that different from Acheron?
It’s pre Acheron