It's a very long fic, something like 50 chapters, I think.
The story starts out with some monsters that generally appear in the north, and it turns out that there's an evil snow goddess.
Every night when Buffy goes to sleep, she dreams of a silent person, and they practice sparring on occasion. We later learn that it was Spike, who had to make a deal with a sleep demon (or demon of dreams, or something like that) and one of the conditions was that he couldn't speak.
In the first part, it's Buffy's POV. The second part shows the same events, as written in Spike's journal. During the third part, Spike and Buffy go into another dimension. Spike is tortured, Buffy rescues him, and at some point they ride on the back of a polar bear. | 
