The D Point was the name of the location and gateway of the Negaverse's own dimension in the Sailor Moon manga and anime. This is also where the final battle between the Sailor Scouts and Queen Beryl (merged with the Negaforce as Super Beryl) took place.
In the anime, D Point was located within the North Pole. In the episode "Usagi's Awakening! A Message From the Distant Past", Sailor Venus and Artemis discover the secret entrance inside the Cafe Crepe. A strange disturbance in the wall led Sailor Venus, Sailor Mars, Sailor Jupiter, Sailor Mercury, Sailor Moon, Artemis, and Luna into a cave that tunneled downward. Luna and Artemis got separated from the Sailor Senshi and eventually came out of the cave into a snow-covered wasteland. They found a purple smoking crater and knew that the volcano was the entrance to the Dark Kingdom. When the Sailor Scouts went to the North Pole a second time, they did so by Sailor Teleport. At D Point, the Sailor Senshi encountered the dreaded Doom and Gloom Girls, 5 powerful Negamonsters sent by Queen Beryl to "greet" them upon their entry to her world. Sailors Jupiter, Mercury, Venus, and Mars were all killed in battles with the Doom and Gloom Girls at D Point. Later after the Negaforce decided to merge with her servant, the new version of Queen Beryl arose and seeks to plunge the planet Earth into cold, permanent darkness. But Sailor Moon along with the 4 Sailor Scouts' help, used the power of the Imperium Silver Crystal and destroyed both Queen Beryl and the Negaforce forever.
In the manga, a disturbance in the form of a heat source was located within the Arctic Circle, which has caused some suspicions. When Sailor Venus killed Queen Beryl, Prince Endymion - still under Queen Metallia's control - took her to the Dark Kingdom's hideout. Sailor Moon chased after them. Luna had trouble scanning the area when she tried to track Sailor Moon. When she was located at C Point, it was said to be 72°N latitude. Luna lost them at D Point, which was in the middle of the Arctic Ocean. Luna then located Sailor Moon in the Dark Kingdom's subterranean domain. This was where the final battle against Queen Metalia took pRelace.
In Sailor Moon - Gaiden Dark Kingdom Fukkatsu Hen, Queen Beryl returned to D Point after her defeat and once more made it her domain. She was eventually defeated there by Sailor Moon's Moon Princess Halation attack.