The Citadel of the Cryu Dzien is a colossal mountain range of solid crystal, with the main peak stretching up into low orbit of the frozen world it was created on.
Inside is a vast city of crystal with street-tunnels bearing majestic arched ceilings and all the amenities one could hope for in a hyper-advanced gigopolis. The population is a little over a billion people, many of them part of the clergy of the Pentatheon, but not all, or even most. At least as many are shopkeepers, engineers, or other skilled workers, and the rest are crew-members of the armada drydocked in and above the mountains.
Speaking of drydocks, the citadel can moor a few hundred large starships (5km +) at a time within the mountain range itself, and has hangers for tens of thousands of smaller vessels near the various surfaces of the mountains.
Overall, the city is very orderly, clean, and easy to navigate even without the aid of computers. It tends to be a bit cold out in the open, but in the "buildings" or public tramways temperatures are more comfortable. While most exposed surfaces are crystaline, not all are. Carpets and more personalized decor are present as expected. The arts are well represented, too, with statues being prominently placed in squares and along streets.
Most guests will primarily visit the Temple district, and more specifically the Temple of the Cryu-Dzien itself, also known as "The Palace." The Palace is like a smaller reflection of the city. It contains both a public section (where worship services and consultations with clergy take place), its own hangers for diplomatic ships, accommodations for guests, libraries, recreational facilities, the banquet hall, numerous small rooms for negotiations, the Goddess's personal quarters, and so on.
