Not long ago we got to see some pictures and announcements via social media of several cast members checking in for filming.
There were shots of Brienne and Pod in what seemed to be their arrival at The Vale.
The gorgeous Carice Van Houten shared a pic of fully costumed soldier Stannis' army in what only seems likey to be Castle Black.
And now the people over at winteriscoming.net have came upon more pics of onset shooting/sighting of several mounted Dornish knights given how their armor/apparel resembles that Oberyn Martell. The crew and cast are reported to be filming at Portstewart (possibly standing for the coast between the Water Gardens and Sunspear).
Possible Spoilers
The follwing picture is a site plan for production, and it might contain some spoilers, for show fiends and book readers alike (given how the show deviates from the books). In it, there are several captions as to what scenes will be filmed and what characters will be present. So, if you are a book reader and still find the show engaging and are pleasently surprisec because of the new scenes that are added, beware.
Inspect At Your Own Risk