What's Your Dark Tower?

Last week, I completed the seventh(and final) book in Stephen King's "Dark Tower" series. Nevermind the 30 or 40 hours I've invested in reading this series, King's masterful storytelling sucked me in once again with the best character development in modern American lit. Not unlike the story of the Hobbits crossing the foreign lands with the ring, King's characters are on the quest to find the Dark Tower, specifically Roland. Roland has crossed a multitude of lands and ages in his quest for the tower, but yet we never really learn what will happen -when- he reaches the tower.
As the seventh and final book drew to a close, we find Roland standing outside the tower, gazing up at the thing he has hungered for since the first word of the first volume. Then, in a way only King can, he breaks in with his own(King's) voice, basically saying, "Shame on you, reader...we all know it's the journey, not the destination. We've loved Roland and the crew since the first sentence, can't you just accept that he's here, but not desire to actually mount the tower with him?" Obviously, we readers cannot! Thus, King begrudgingly allows you/me, the reader, to follow Roland to his final quest. Since no one spilled the beans to me as to what happens from there, I won't spoil it for you either, MY faithful reader.
Still, this whole scenario made me think-Roland's entire life was spent in search of the Dark Tower. It motivated him, fed him, it became his number #1 desire and carried him through situations so dire that, even though we know are fiction, still scare the beejesus out of us.
What's your Dark Tower? What is that thing that drives you? What makes you put one foot in front of the other every morning? What makes you not give up, even when it feels like the earth is crumbling in on top of you?
Everyone has their own answer to this...and DT #7 made me do some soul searching for mine. What is that? Another time, faithful reader...another time.