In "Midnight Scrum"
"Midnight Scrum", an episode in Dragons: Race to the Edge, Season 4, starts with Hiccup running from a number of other Vikings of unknown origins. Toothless, Astrid, and Stormfly save him from being caught. They find out that Viggo Grimborn has placed a sizeable bounty on Hiccup's head. This island appears rather large with mixed forests of deciduous trees with spear-shaped leaves and conifers. There are ample grassy slopes. Toothless is seen carrying a bucket of harvested ripe red apples.
In "Not Lout"
In the Dragons: Race to the Edge, Season 4 episode, "Not Lout", Hiccup discovers the source of the Dragons Hunter's abundant supply of Dragon Root arrows. They have a farming operation on this unnamed island. However, what Hiccup takes to be a plot of hidden Dragon Root plants under a camouflaged canopy, actually turns out to be large arrow-shooting weapons. Snotlout, having stayed behind on this mission, realizes that the canopies may be a trap, because Dragon Root plants require sun to grow, not shade. The island is large with two snow-topped mountains and sparse wooded areas, some of which might be Dragon Root trees. The Dragon Hunters have established several buildings for farming and processing Dragon Root here, as well. The island also has at least one beach and docking area for ships.
In "Saving Shattermaster"
The Dragon Hunters sell the Iron Masons a large number of Gronckles, presumably so they can make Gronckle Iron. Dagur the Deranged, Hiccup, and Heather follow a ship to the island of Iron Masons to find the Gronckles and therefore Dagur's dragon, Shattermaster.
This island is crescent-shaped with a large harbor in the curve. There is a large smelting and forge facility on the island and little else. It does have grass and tall trees.
In "The Longest Day"
During the Midnight Sun in the Barbaric Archipelago, a very tired Hiccup and Toothless hear a distressed dragon calling from an unnamed island. However, the distressed dragon, a Small Shadow, was just a ruse to lure humans and dragons to the island for dinner. Hiccup also discovers an abandoned Dragon Hunter camp in a cave in the island.
The island has caves and canyons, and one central mountain that appears as if its peak has been sheared off. There are deciduous forests, bushes, and grass. There are also sandy beaches suitable for anchoring a ship.
In "Gold Rush"
In "Gold Rush", an episode in Dragons: Race to the Edge, Season 4, Dagur the Deranged shows up at Dragon's Edge with intel about where Viggo Grimborn hides his gold. Some of this is the gold that was stolen from Berk. The Dragon Riders go to the unnamed island and search everywhere for the gold but are unsuccessful. Eventually, after an encounter with the Dragon Hunters, Hiccup deduces that some old Viking ruins on the island are actually the gold in disguise.
The island is rather verdant with deciduous trees that have light-colored bark, grassy meadows, and bushes that have large, daisy-like white flowers.
In the Dragons: Race to the Edge, Season 4 episode "Twintuition", Ruffnut and Tuffnut venture to the Northern Markets to fix Tuffnut's mace, Macey. The twins end up on a Dragon Hunter ship that takes them to the secret base of Project Shellfire.
The island appears to be rocky and fairly barren with the exception of some leafy trees. It has an artificially constructed pit next to a bay, that can be flooded with water once Project Shellfire's ship is finished construction.
Location One in "Living on the Edge"
In this episode, Krogan captures a Death Song from Melody Island and uses him to capture even more dragons. Krogan and his forces stop at an unnamed island and capture many dragons such as the Deadly Nadder. They also capture a Singetail, which he is very pleased about.
This island has deciduous-appearing trees, rocky ground, a beach area, and also tall coconut trees.
Location Two in "Living on the Edge"
In this episode, Krogan returns to this location with a captured Singetail. He appears to have his own dragon arena of sorts. The brief glimpse of the terrain is dark and barren, similar to how Outcast Island appears. It doesn't seem to be any vegetation there.
The episode "Return of Thor Bonecrusher" begins with Krogan going to this quaint but seedy tavern in a forest. It is positioned against a rock cliff and seems to burrow into it. The interior likewise appears as if in a cave, and rather large. Krogan is there finding a certain villain to join forces with - Viggo Grimborn.
This island appears to have a flat rocky coast rather than beaches, grass, and a horizon of barren trees. The Dragon Riders stopped on this island only briefly to catch their breath as they fled from Dragon's Edge and being chased by the Dragon Flyers. They did not get to rest long here, as the Flyers caught up with them quickly and chased them away. The Riders flew on to Berk and relative safety.
In "No Dragon Left Behind" and "Family Matters"
In the Dragons: Race to the Edge, Season 5 episode "No Dragon Left Behind", the Dragon Riders relocate Garff to a new island, after unsuccessfully trying to move him to Slitherwing Island. The new island is mountainous, has sandy beaches, and trees and shrubs.
In "Sins of the Past"
This location appears to be a collection of rocky outcrops and large Sea Stacks, some with shorelines. It is located near the island of the Northern Markets. Krogan and his Dragon Flyers chase Heather down, along with Snotlout, Hookfang, and Trader Johann. Windshear has been captured, and Hookfang is unable to carry everyone and needs to stop to rest. The group is essentially stranded on these sea stacks. Krogan presents a decision to Heather: Windshear or the Dragon Eye lens on her belt.
In "In Plain Sight"
In the first episode of Dragons: Race to the Edge, Season 6, Dagur the Deranged helps a childhood acquaintance, Ansson, catch the mythical Thunderfish in exchange for a Dragon Eye lens. The Thunderfish turns out to be a Scauldron.
The area of sea located in the fishing areas of the Berserker Tribe contains sea stacks. Ansson baits the Thunderfish in a narrow straight in between two sea stacks.
In "No Bark, All Bite"
In the second episode of Dragons: Race to the Edge, Season 6, "No Bark, All Bite", Stoick learns of Johann's treachery and burns all the provisions obtained from him, including medicines. This leaves Berk without any willow bark. Stoick and Hiccup leave to go find some themselves, armed with a map from Gothi showing which islands have the willow tree. Only two islands are seen.
At each island they travel to, the Dragon Flyers follow them and fire on the islands.
Location One in "A Gruff Separation"
In the Dragons: Race to the Edge, Season 6 episode, "A Gruff Separation", the Twins must complete three challenges as part of the Thorston Induction Trials on their 19th birthdays, to become full members of House Thorston. The first challenge is to collect the venom of a Speed Stinger.
The island the Twins go to is forested and rocky, with a tall, thin central mountain. There are also sandy beach areas.
It is possible this location is actually Speed Stinger Island, though it is not specifically named as such.
Location Two in "A Gruff Separation"
In the Dragons: Race to the Edge, Season 6 episode, "A Gruff Separation", the Twins must complete three challenges as part of the Thorston Induction Trials on their 19th birthdays, to become full members of House Thorston. The second challenge is to collect the shed skin of a Changewing.
The island the Twins go to is heavily forested and rocky. It also has sandy beach areas, as well as at least one lake area, and flat-topped rocky pillars.
It is possible this location is actually Changewing Island, though it is not specifically named as such.
Location Three in "A Gruff Separation"
This island appears in "A Gruff Separation" as the location of the third challenge of the Thorston Induction Trials for the Twins. The island is mountainous and riddled with caves. It is also the lair of a Titan Wing Zippleback and its pack. Treasure and a small treasure chest is hidden in the cave, and the Twins must retrieve it. Only one will win the Trials, however.
Location One in "Triple Cross"
In the Dragons: Race to the Edge, Season 6 episode, "Triple Cross", Viggo is double-crossed and left for dead in a cave, after Johann orders the cave to be sealed before he can get out. He is saved, however, by a Monstrous Nightmare who is also in the cave. This dragon's altruism leads Viggo to have a change of heart and respect dragonkind.
This island appears rather flat - but still very rocky - from the air, compared to other islands. There is, however, a fairly extensive cave system underneath, with an abandoned camp within it. There do not appear to be many trees on the island.
Location Two in "Triple Cross"
In the Dragons: Race to the Edge, Season 6 episode, "Triple Cross", Viggo has Hiccup stop at an unnamed island on their way to infiltrate the camp Johann and Krogan are at. This island turns out to be the home of a Skrill. Viggo's tames or gentles it in a rather simple manner. The Skrill then accompanies Viggo and Hiccup to the island Johann is at.
This island has a single spire so tall that it reaches low, stormy clouds and has a snowy cap. Its lower portion seems to be vegetated with grass and trees. There are also bare trees at its apex. The island is also surrounded by a number of sea stacks.
Location Three in "Triple Cross"
The episode "Triple Cross" shows another island with a robust Dragon Hunter outpost within a large cave system. It is here that Viggo Grimborn attempts to help Hiccup in his way and get back at Johann and Krogan for abandoning him on the previous island in this episode. While he is helping Hiccup and his Skrill escape, he is struck by several arrows and then takes a final stand against a wall of archers.
The island itself is mountainous and forested. The interior of the cave system has a complex of booby-trapped treasure rooms, meeting rooms, dungeons, and extensive shelves of papers and maps.
Location One in "Family Matters"
A large portion of the Dragons: Race to the Edge, Season 6 episode, "Family Matters", takes place on an island containing a Dragon Flyer camp with a Singetail Hatchery. The Flyers use a Death Song to catch Singetails as they come and go from their eggs. There is a presumably man-made circular depression at the center of the island with a network of caves in its face. There is a set of caves for human needs, and another cave system housing the Singetail hatchery. The island itself is situated near other islands. It is surrounded by a number of sea stacks.
Location Two in "Family Matters"
Fishlegs lures the Cavern Crasher over to the island near by with a Singetail egg. The island has a Singetail hatchery on it. The Riders use the Cavern Crasher to burrow another tunnel out, as they are trapped inside a cave with Dragon Flyers blocking the entrance. Snotlout takes the Singetail egg and lures away the Cavern Crasher again, as the rest of the Riders escape and free dragons.
It appears to be small, relatively flat, and rocky from the air. There appears to be little to no vegetation present. It is not clear what is available for the Cavern Crasher to eat.
While chasing down Dragon Flyer scouts to stop them from telling Johann about Vanaheim, the Dragon Riders encounter a thunderstorm and are chased through it by the Flyers. They take refuge in the shipwreck, while Hiccup comes up with a plan to escape and take down the Flyers. Later, utilizing old Bolas and the lightning to zap the Flyers from their mounts, the downed men swim ashore on the small island with no way off it.