Vulbaal

The capitol of the Deluvian Empire, Vulbaal (meaning 'City of Blood' in Kuar) is the seat of power of a massive and ancient civilization. The most notable landmarks are the ancient Imperial Palace (both highly fortified and opulently furnished), the Mun Baru temple (a massive step pyramid, on a scale similar to Earth's Great Pyramid of Giza), and the infamous Ulbu Road which runs between them - a straight [I forget] mile long road lined with the skulls of many other races, all surfaced with an inch-thick layer of solid gold, which even extends up the staircase to the top of the stone temple. Slaves, traitors, or other victims of conquest are sacrificed atop Mun Baru every day, but on the Day of the Divine Gift every four years, slaves are sacrificed in such obscene numbers that their blood runs down the golden stairs, all the way down the Ulbu Road to touch the first step of the Palace.
Like most of the greatest cities of the amphibious Kua Toa, Vulbaal was built on land, where the majority of their aquatic slaves can't survive for more than an hour or two, making it nigh unassailable by any slave revolt. Vulbaal is unique in that sense, as its massive wealth and population "require" a great many slaves, and since air-breathing slaves are so rare (and have been intentionally and genocidally kept rare), Vulbaal actually contains the greatest single population of the fully-amphibious Aventi species that remains in the world. However the level of military power retained on paranoid standby, plus obligatory SlaveHunters, and deadly Monitors, are such that there is considered to be no chance of any significant action by the heavily repressed enslaved peoples.