A Hellgate, as seen in Episode 1 of Season 3.
Hellgates, or portals, are gateways made of obsidian that lead to The Nether. They seem to be linked to the source of The Sands, as well as Israphel and his cult; and is also one of The Dark Constructions. They are dangerous, as they produce the Sand where they are placed, and are currently used by the Cult of Israphel to attempt to spread the Sands in the lands beyond The Wall. The first gates were created by an unknown civilization.
In chronological order, they are:
The Ancient Hellgate[]
This Hellgate was discovered by Professor Grizwold, before The Sand War, inside The Ruined Castle,as he was research the ancient civilization that created them. He accidentally activated it, causing monsters and darkness to start pouring out of it. The activation of it also activated ancient giant signal fires, (which may have been later used for The Wall) and caused both a giant meteor to strike the area, and other disasters, as well as causing monsters, such as viners (the early name for creepers), to appear. It was destroyed by Verigan Antioch and his band of adventurers. It is unknown why this Gate cause such damage compared the others, causing natural disasters, though it is the only confirmed Gate seen that was created by the ancient civilization.
The First Ruins Hellgate[]
Built by the Cult of Israphel that was based in the Crumbling Ruins outside Mistral City, inside said ruins, it was discovered and destroyed by Karpath Peculier, possibly alongside other members of Mistral City's guards. The remains of this gate were later seen by the Yogscast.
The Mine Hellgate[]
This Hellgate, built in the mines under Mistral City, was also destroyed by Karpath Peculier, using explosives, after he walked through it to seal it shut. The existence of this portal was covered up, and the mine was closed as a result. Discovered many years later by his son, Old Peculier, and the heroes, Honeydew, and Xephos.
The Hellgate of The Cave of Terror[]
Built by the unsuspecting heroes, this Gate was how Israphel returned to the world. Used by Israphel later as an escape route from his Castle, he also took the kidnapped Daisy Duke with him through it. When Old Peculier saw it, he said, "Who would have been stupid enough to build a hellgate?" Simon and Lewis said, "I don't know." Destroyed by Xephos and Honeydew at the beginning of Season 3.
The Second Ruins Hellgate[]
Built in the same chamber as the previous Ruins hellgate, it was destroyed by the Yogscast. There were many cultist's guarding this Hellgate, including the zombified Granny Bacon, and Reverend John.
The BBQ Bay Hellgate[]
Found in a cave underneath BBQ Bay, and linked to Jock Fireblast's ship, it was presumably built by Jock. The Yogscast entered this portal, fleeing from monsters and a trap activated by Jock, it lead to a metal box located in The Nether, much to our protagonists surprise, supposedly constructed by a highly advanced, possibly ancient company known as "N-Comm". The box had signs about the gate being a time-space portal, possibly similar to a TARDIS, as theorized by the Yogscast.
The Stoneholm Hellgate[]
Built by King Finbar on top of the spire generator connecting to Stoneholm through the Deepcore. It is used by Finbar to redirect the spire's energy from The Wall to the N-Comm Systems JADE SENTINEL Central Power Core, presumably to allow Israphel to invade Minecraftia. The Stoneholm Hellgate presumably caused the large anomaly to appear on top of the spire.
The Lastwatch Hold Hellgate[]
Presumably built by Israphel or King Finbar, the Lastwatch Hold Hellgate stands by itself in The Desert near the ruins of the wall bastion Lastwatch Hold. It connects with the Stoneholm Hellgate through The Nether via the N-Comm Systems JADE SENTINEL Central Power Core.
The Roller-Coaster Hellgate[]
Built by unknown builders, it is located under the roller-coaster near Verigan's Hold, and connected to the JADE SENTINEL Central Power Core. It's Minecraftia side lead into a secret chamber which was used by the Carnivale Del Banjo, who entered using a hidden entrance in Madame Nubescu's fortune telling chamber. It was used by our heroes to escape as the Power Core started to explode. It was already slightly destroyed.
Possible other Hellgates[]
There may be other hellgates, as both Prof. Grizwold and a young Fumblemore expressed interest in finding more Gates built by the ancient civilization