I have been researching some of Tibia's more curious quests and stumbled upon this hidden gem, the Waterfall Quest.
Out in the jungles of Port Hope you can find a hidden drop hole located here:
(original source of this image taken from tibia wiki.com)
Travel through this drop hole and up the holes unto you reach the waterfall.
Head into the waterfall and swim through the hidden tunnel to find the quest reward within.
As you can see, this place is a very unique place with the level of effort put in its design from multi level map use to swimming/teleporting and detail given to the location itself. Tibia wiki also says this on the location ' LEGEND: A pirate forgot his treasure in a cave in the waterfalls near the traitorous nest of the feared Hydra.' However, doesn't indicate any actual source or book that might reference the location in game/the legend given.
There is also a npc located fairly close to the entrance of the waterfall location, NPC The Blind Prophet. However, I checked his transcripts and he doesn't seem to mention the waterfall/pirates/the tunnel.
I am really interested in this location and figured given the amount of effort Cip put into the location there must be some mention or reference of this quest and its story in game.