Isle of Lost Vikings is a location seen in Dragons: Rescue Riders.
The Isle of Lost Vikings is mostly a forested area, with several cliffs and two lakes in the middle of the island. Its most prominent feature is a system of underground tunnels and caves, filled with booby traps by vikings. One of the entrances is located at the edge of a forest, while the other opens to a beach surrounded by Sea Stacks.
In "Treasure Riders", the Rescue Riders, Marena, and Waldondo del Mundo went to the Isle of Lost Viking in search for Odin's Gem. They ventured inside a cave full of booby traps, but managed to survive thanks to the dragons. When they emerged from the other side, they ended up on a beach, where a viking ship was located. However, the whole thing was a setup, as Waldondo planned to capture the Rescue Riders. He trapped Marena and left her on the island, after which he sailed with the dragons locked under the deck.