Oracle of Apollo (Location)
A special sort of temple in the Green Mountains.
The scroll is up in the Oracle chambers.
Inside, find it on the floor, next to some other scrolls and a box of bottles.
Claiming it grants the Wet Work riddle, and completes the location.
Note that you can talk to the Oracle for the Halo of the Huntress side quest, as well as dozens of other intriguing prophecies.