Tharbad's demise may not present that much of a mystery to the C7 writers. In addition to the floods, the people of the city also suffered for centuries from the wars that ravaged the area (the Witch-king's destruction of the North-kingdom, etc.), as well as the plague.
It can still be a cool side for an adventure, however, because during its waning days, & certainly after its 'abandonment': Ruffians may lurk within the ruins, searching for lost treasures & the like; as can renegade Dunlendings; Saruman's spies; & so forth. They can work separately or together (or at least cooperate as much as any servants of the Enemy cooperate
![Wink ;)](images/smilies/icon_e_wink.gif)
), & you can also have your heroes just plain search for treasure as well. Perhaps Elrond or Gandalf ask them to find some ancient Dúnedain or Elven heirloom within the ruins?
Ditto for Ost-in-Edhil for that matter. There are at least two ways to look at the Noldorin fortress:
1. The Elves built so well that at least some of the ruins yet survive, & perhaps Sauron didn't find everything when he scoured the place? Yes, that's a stretch, but it's a game
![Smile :)](images/smilies/icon_e_smile.gif)
.
2. The fortress does not survive the years in any more than a rudimentary form, but a treasure or two yet remain...