The Nine And The Nest

Searching for something, we find other things of the same name. Searching this blog discloses that there are two groups called the Nine and two places called the Nest, three of the latter if we include Yotl's Nest (scroll down), a multi-species bar in another civilization-cluster in After Doomsday. This in turn displays the breadth of Poul Anderson's imagination. The two Nines and three Nests are scattered across:

"Time Patrol," the opening story of the Time Patrol series;

the King Of Ys Tetralogy, historical fiction with an element of fantasy, co-written by Karen Anderson;

"The Nest," a time travel short story;

The People Of The Wind, one volume of the History of Technic Civilization;

After Doomsday, an sf novel.

In The People Of The Wind:

The Nest, a tavern for ornithoids, is the tallest building in Centauri with a gravshaft to its rooftop for humans who have not brought flying gear. It is unwalled, protected from rain by a vitryl canopy. Insectoids circle fluoroglobes and a service robot serves New African beer.

-copied from here. (See: In The People Of The Wind, Chapter Six.)