The Moon Kingdom
The Silver Millennium, though it had a fairy-tale appearance, demonstrates an advanced technology. It existed within a dome which produced an artificial climate, and had an advanced computer called the "Eternity Main System". According to Artemis, ice skating was very popular there. Those who lived in the Silver Millennium had very long life spans and had two specific duties: First, they were to protect the Silver Crystal, an extremely powerful "holy stone" which had been handed down through the generations. Second, they were to watch over the evolution of Earth and protect it from any negative influence.
During this era Endymion, flanked by his four guardians, held the position of Crown Prince of Earth. Despite a prohibition on relations between people of the Earth and the Moon, he and Princess Serenity fell in love. Out of jealousy and under the influence of the evil Queen Metalia, a peasant woman named Beryl raised up the citizens of Earth in a war against the Moon. Warfare completely wiped out both kingdoms, so the evolution of life had to restart from the beginning.
Before dying, the Queen sent her daughter and Endymion for rebirth on Earth during the 20th century. They become Usagi Tsukino and Mamoru Chiba and, even before they recover their memories, succeed in finding each other once again. The Sailor Senshi also undergo rebirth, becoming close friends; through their efforts, the reinstated Dark Kingdom and even Metalia herself are destroyed. In the manga, the Moon Kingdom and its castle are "resurrected" at the end of this conflict, but Usagi decides to continue living on Earth, with her parents and with Mamoru.
Both the anime and the manga reveal that a new Silver Millennium will exist in the 30th century, centered in the city of Crystal Tokyo. Usagi and Mamoru will rule it under the names of Neo-Queen Serenity and King Endymion, and they will have a daughter named Princess Usagi Small Lady Serenity.
The Guardian Senshi protect not only Neo-Queen Serenity, but the entire royal family. However, the story makes no mention of the location of the Outer Senshi, other than Sailor Pluto. After their awakening in the manga, the Sailor Quartet also act as guards, but to Small Lady. Luna, Artemis, and Diana live in the palace as well.
At the center of the kingdom lies the Crystal Palace, where the Royal Family and the Guardian Senshi live. The manga depicts it over water, while in the anime it has another palace, Serenity Palace, located at the top middle spire. It is particularly shown in the beginning credits for the second opening sequence of Sailor Moon R, and is seen in a flashback where Chibiusa thinks that the Guardian Senshi and her parents have forgotten her birthday. Later, the interior is shown, indicating that this is the part of the Crystal Palace where the Royal Family and their protectors live.
Exposure to the Silver Crystal renders all of Crystal Tokyo's inhabitants functionally immortal. Anyone not born there becomes essentially locked at their current physical age, as shown by the Queen and King and their court, who all appear as if aged in their early twenties. Anyone born in Crystal Tokyo has a slow growth-rate — Small Lady, for example, is stated in the manga to be over 900 years old, yet has the body and mind of a child. According to her parents, such an extremely slow growth is irregular, and Chibiusa's extended childhood is an important part of the fourth plot arc.
The series depicts the Sailor Senshi of the 30th century in their original uniforms, without any of the enhancements or powerups they gained in the latter part of the series. At the time the plot arc was drawn, Takeuchi had not yet introduced the idea of enhancing the Senshi uniforms.