So I randomly discovered Sunderstone Gorge and cleared the dungeon. Next to the Fire Breath word wall, there is a large treasure chest. Not knowing anything, I just hit "R" (playing on PC) to loot the entire contents of the chest.

So many many many hours later as I was back at Breezehome, ready to organize my loot, I noticed that somehow an undroppable quest item slipped into my inventory. It is a book called "Hanging Gardens" which I found in that chest in Sunderstone Gorge!

So now what? There are no quests related to this book in my quest journal... now how am I supposed to find out what to do with this book!!?

I can't revert to a previous point because it has been many hours since I found the chest - saves were already deleted/overwritten as I regularly maintain a clean save directory.

its probably for a misc quest for the librarian at the CoW. Thats where most quest books go.

because youve found the book before getting the quest, youll have to use the console to get rid of it. its one of those 'broken' quests.

What is the console command to do that? Also, if after getting rid of the item via console; I eventually decide to start the quest legitimately, will it still work as normal, or am I permanently screwed?

You can find that here:

http://uesp.net/wiki/Skyrim:Console

Use the command

player.removeitem 1ad08 1

It shouldnt ause you too many problems later on should you happen to get this misc. quest in the future - worst case, you will have to setstage with console later on. no biggie.

Thanks Aphaea!

I have this very same issue with the, "Finding the Remada (or whatever it is) book quest." I found the book a long time ago before I got the quest and it's been sitting in my inventory. The quest still points to the busted ship's hold and the chest where I found the book. I can't advance the quest any further. I forgot all about the "SetStage" console command. I'm going to have to do that now. Thanks.