George R. R. Martin is once again posting HBO casting items as elaborate riddles (the commenters on his blog are surprisingly good at reading between the lines and trawling IMDB until they figure out the item), and the answer has been revealed: Gwendoline Christie, late of Terry Gilliam's ingenious mess "The Imaginarium of Dr. Parnassus," will play Brienne of Tarth in the second season of "Game of Thrones."
Brienne, a would-be knight who's arguably a better person than most of the actual knights in "A Clash of Kings" and following, is actually my favorite character in the books; the only bone I'd pick with the casting choice is that she's supposed to be very ugly, and Christie is kind of striking and willowy. She's super tall, though (6'5", see photo for comparison), which is good. And the lovely Natalia Tena has certainly been dressed down to play Osha. Still: start lifting weights, Gwendoline.