From the back cover:
Welcome to the city of twilight, the city of thieves, the city among the stars. Founded by pirates, Bral is now a prosperous city of rogues and merchants, adrift in the vast realms of Wildspace. Its docks are crowded with graceful ships, its streets are teeming with intrigue and adventure, and its population includes shining heroes and dark villains. The Rock of Bral is a haven for any adventurer with a quick wit and a dash of greed - opportunity only awaits the hand bold enough to seize it.
Rock of Brak is an accessory to the Spelljammer campaign setting and is intended to provide a ready gude to this most fascinating of cities. Your character will find the Rock to be the perfect base from which to explore the magical reaches of Wildspace.