Established in the no-man's land between the territory of Amber and Chaos, the Green Griffin is the premier cross-shadow gathering place. Here those from both poles of existence mingle with the denizens of shadow. It is de facto recognized by both governments, having been used for several of the post-Patternfall negotiations.
Those inside its walls are under Chorovius and Roland's protection; violence against them is met with quick and severe retribution. If confronting the combined forces of a Pattern initiate and a Logrus master on their home ground wasn't bad enough, there are persistent rumors that they have covert support from major players on both sides of the fence. It's been years since anything was attempted by those in the know.
The Green Griffin is a floating castle. The shadow it floats around is lush and apparently unpopulated. It is presumed that Chorovius can control the direction of the float, but this has not been verified. It has 20th century plumbing and electric power. Banquets, dances, and concerts frequently grace its halls.
[If you've said "Castle Black" by now, you've got good taste in reading material. The basic idea obviously owes a lot to Mr. Brust.]