Also known as Dor-Erthenos, the Diamond Realm is the kingdom of the Giants, located in the fertile river basin of the Ghostwash and its tributaries. The island city De-Shemod is its capital, a stately metropolis with soaring, monumental architecture. Here you will find the Council of Magisters, several Warmain academies, and of course the Diamond Throne itself.
In the lands beyond De-Shemod the Giants have established fiefs, ruling over Human serfs and Jackal-Kin lackeys. Loyal Humans are rewarded with aristocratic titles and lands of their own; by and large the Giants are condescending but not tyrannical.
In terms of aesthetics, I imagine the ruins of the earlier human habitation to resemble traditional European Gothic touches, while the Giants, who came from a desertous land over the sea, might have a more Egyptian or classical style.
The Diamond Realm's major political rivals are the hordes of Chorim (militaristic ogres in the mountain valleys) and the wild tribes of the Waste Lands. The Fairies of Harrowdeep are allies, but not always trustworthy, and perhaps grow suspicious of the Giants' pre-eminence. The city-states of Fallanor are too distant to present a serious threat, but they do have an economic importance owing to shipping. There are also problems within the Diamond Realm involving revolts.
Wizards and Warriors
The Giants possessed several cultural advantages: their magicians, known as Magisters, wield tremendous powers, and their heavy infantry, known as Warmains, are exceptionally well trained. With the twin advantages of sorcerous skill and military might the Giants managed to drive off the Dragons, and established the Diamond Realm as the preeminent "superpower" on this continent.
The Magisters are taught in several refined academies; these are places of great learning and scientific investigation.
The Warmain academies take pride in their legions of elite soldiers, and each academy has its own specialized combat style, often with colorful names, and they have a rivalry against other schools.
Diamond Realm Cultural Skills
Craft: Fortify (V)
Diamond Realm Cultural Secrets
Three-Corner Magic Secrets
Treat these as the magical style of the Magister. They are described in the Shadow of Yesterday world book.