The N-Comm JADE SENTINEL Central Power Core is a metallic structure in The Nether which contains two Hellgates, one connecting to The Spire, which reinforced The Wall, and the other one at the ruins of Lastwatch Hold, which is deep within The Desert.
It is unknown who erected it, although it was probably created by the same person or group of people who built the Experimental Space/Time Fissure Number 8. From its name, it is possible to have been built by the company called N-Comm. At some point, it was refurbished by the Cult of Israphel to create a passage between The Desert and the outside world. The Hand discovered in the desert may belong to a Jade Sentinel, but there is no confirmation.
Originally, as the name suggests, it may have been used by N-Comm to power all of their other Space/Time capsules, such as the Experimental Space/Time Fissure Number 8, and possibly Jade Sentinals. It was, however, apparently in some way very dangerous, as, by protocol, it was only to by used in an end-of-world Scenario.
After the Cult of Israphel took it over, King Finbar built a Hellgate connecting it to the generator reinforcing The Wall, creating and immense tactical advantage for Israphel. Using the spire's power, he managed to activate it briefly before he was stopped and killed by Knight Peculier (with help from Xephos and Honeydew). During the fight, Finbar accidentally destroyed the redstone power supply coming in through the Hellgate, but not before it was activated. According to readings in the control room, it will become fully operational in three days and seven hours from Finbar's death. After said time, should it become active, it would awaken the Dark God of the Sands, who would choke the world in sand.
Much larger than the previous metal box explored by the Yogscast, the JADE SENTINEL Power Core contains multiple rooms. The first room seen was the control room, which housed King Finbar's Hellgate, and had a huge array of monitors shining in the shape of a Creeper face. During Finbar and Peculier's battle, a shaft was opened up that led to a large corridor, connecting to at least four other rooms.
These included a viewing room which looked out upon a "Lakeside Portal," a large iron block which could possibly be the Experimental Space/Time Fissure Number 8, the Core Processing room, which is made inaccessible by a lava flow, the Antenna Array, which was blocked off by a dirt barricade, and an unnamed room at the end which opened up to The Nether, and contained an undamaged but unactivated Hellgate frame, which, after being activated by the heroes, led into the depths of The Desert, near the ruins of Lastwatch Hold.
There also was another corridor, that led to unknown other rooms, which was blocked off by a netherrack wall. A third path was opened when the heroes re-entered the power core, which seemed to somehow be going into a melt-down, explosions wracking the place. The new path, broken though it was, lead the heroes to another Gate, this one oddly working despite damage, that lead to the area underneath the roller-coaster, just outside Verigan's Hold.