Currently, the only known Dragon Waste in the world of Girl Genius is the one created by Hydrargyros before his (ahem) untimely passing. This is thus part of the Wastelands, dangerous areas that exist almost everywhere between the more heavily populated areas of Europa.
It is located a fair distance from Mechanicsburg; it takes an overnight train ride on the Corbettite Railway to get to a gateway ✣ which allows entrance. And although Hydrargyros had a weak flame, he also had the Iram Solis, a Spark-created super-powered flame amplifier, which means that the Waste is quite extensive and dangerous; even the Wulfenbach empire at the height of its power avoided the area.
One of the dangers of the Waste are large and voracious Ash Eels.
In the middle of the Waste is a former subterranean city of the "Mountain Kings", beneath which is Hydrargyros' Hoard. It is this Hoard which Vipsania Perrault, Franz Scortchmaw and their various companions set out to claim. It contains valuable books long thought lost, as well as conventional treasure (and the Iram Solis, of course).