Béy Sü is the capital of Tsolyánu, a sprawling metropolis with over a million souls*. The name means "Soul of the World". It lies on the banks of the Missüma River about a thousand tsán north of Jakálla, Tsolyánu's next largest city*. The main part of the city lies on the western shore of the river; on the eastern are a few temples, some villas, the Necropolis (or City of the Dead) and the dreaded Tólek Kána Pits, the Imperial prison.
This picture is from the cover of the original game box that the Empire of the Petal Throne RPG (EPT) came in, way back in 1975.
* at least IMT - "In My Tekumel"! :-)