The Dream Prison
The adventurers must travel to the Plane of Reverie and free an ancient heir to a dying kingdom from the Dream Prison. Along the way, the heroes must sail the Sleeping Rivers, defeat the threshold guardians, and unbind the prisoner from a sorcerous jail.
An original level 6-8 adventure made for D&D 5e.
Available here: https://www.drivethrurpg.com/product/335416/The-Dream-Prison?affiliate_id=14013