Alone on the water was definitely the saddest fics I've ever read. While is disagree with how some of it would have gone (I'm not a Johnlock shipper, at least not it a romantic way) I thought it was well written and heartbreaking.
Sherlock/Doctor Who (Tick Tock) I cannot express how much I love this pin. This is amazing. You think the Sherlock fandom is all Photoshopping food into Moriarty's hand during dramatic moments and then you find stuff like this and you remember the brilliance of this fandom.