A while back it was announced that actor David Schofield (Merlin's King Alined) was set to take on a rather mythical, regal role in the show, as Norse God Odin. This suggested that the Doctor would be in for a bit of a viking adventure, and the trailer has now seemingly confirmed this. While the image above may not be of Odin, it's clearly a viking of some sort, accompanied by a couple of unknown, large robotic beasts. It seems likely that this will tie into the two-parter The Girl Who Died / The Woman Who Lived, as they're the ones that Schofield was confirmed to be appearing in. Vikings have appeared in Who before, back in the 60s, but that was a more historical take, whereas this looks like it'll be a more upgraded version; space-vikings, as it were. At Comic-Con, Capaldi gave away this little snippet, which means we can expect to see far more than just the solitary one above: "I walked in and saw in a space suit on a spaceship with a pile of vikings. It just looked absolutely amazing."