Location from Sailor Moon by Naoko Takeuchi / Toei Animation
The ancient lunar civilization that flourished in the age of the Silver Millennium — ruled by Queen Serenity, home to Princess Serenity and her guardian Senshi, destroyed by the Dark Kingdom's invasion.
The Silver Millennium was a prehistoric civilization on the Moon, where Queen Serenity ruled with the Legendary Silver Crystal and the Sailor Guardians of the inner planets protected the Princess. Life was long and the Crystal kept the peace. The Earth was off-limits — its people were considered fundamentally different, earthbound, mortal. Princess Serenity crossed that boundary for Prince Endymion. Queen Beryl and Queen Metalia destroyed the Kingdom for reasons that included that love and were larger than it. Queen Serenity used the last of her power to send the survivors forward in time, to be reborn, to have a second chance. The Moon Kingdom itself was left behind in ruins that the present-day Sailor Guardians visit once in vision and don't talk about afterward.
Gleaming white castles and spires on the surface of the Moon, under a dome of perpetual light. The Moon Castle — Serenity's Palace — dominates the skyline. The world is quiet and permanent-looking in the way things are before they break. Most of what the present-day characters see of it comes in vision and memory, silver-lit and achingly beautiful.