This is intended to be a setting seed for some future story or game, like The Chapel of Weeping.
There was once a theater on a small island set in the river’s delta. Some of it remains. The city it was part of fell ages ago; after the city was sacked by a victorious army its people fled, were captured, or were put to the sword. The theater escaped the initial destruction, and was protected from the fires that raged through the city by its watery border. As such, it is one of the few places in the ruined city which still bears the clear marks of its builders. Unlike most other places in the destroyed city, none of the theater has been scavenged for building stones.
The theater’s finery was stripped by more organized looters after the sack. No surviving city folk or other locals participated in looting that theater, however, for it was said to be holy. Indeed, the vessel used by the looters sank in a freak storm several days after reaching port.
Rumor has it that the people who took the theater’s riches each suffered exquisitely awful deaths, and each family of theirs which did not dispose of the treasure soon fell to similarly terrible fates: slow wasting disease, all-consuming madness, cruelly ill luck. Whether or not this is true is widely debated, but these stories are favored by those who still live near the fallen city. They’re also popular as ghoulish legends amongst the descendants of those whose forces ruined the city so long ago.
The queendom which sacked the city, and whose people looted the temple, has since fallen into decline.
The theater, when it still stood wholly intact, was said to have a very particular ceiling. Intended to magnify moonlight, it captured the moon’s beams to light the floor of its amphitheater, at its brightest on the most holy nights of the moon’s phases. It is said that the theater could transport its audiences to unknown heights when the sacred plays were performed on the proper nights, but it is not known what those plays were, which nights those were, or whether the “heights” referenced were emotional or literal.
There are no publicly known survivors of the theater’s cult. It is a puzzle which has intrigued many for centuries.