The Northern Markets first appear in the episode, "Saving Shattermaster".
This island appears to have a bustling market of sketchy Viking traders and weapon-smiths. The land outside the markets, however, appear to have healthy grass, trees, and other vegetation, on a hilly and mountainous island. There is at least one area along the shoreline suitable for docking ships.
Dragons: Race to the Edge
The episode, "Saving Shattermaster", opens with the Defenders of the Wing attempting to buy weapons at the Northern Markets. There is a shadowy figure lurking there that appears to be working with the Dragon Hunters. Upon investigation, the Dragon Riders discover Dagur the Deranged is at the Northern Markets, posing as a friend of the Hunters. His real goal, however, is to save Shattermaster from slavery.