A world with a desert-like surface, Aleen was unique in that it contained a series of complex caverns in its upper crust. These were considered to be part of a distinct subterranean biome with its own unique atmosphere. Formed by the growth of the native arbozoic trees, the caverns were built-up of tunnels carved by water, lava, and tectonic shearing. Fostering a separate climate, and an atmosphere that was toxic to the surface-dwelling Aleena, the planet’s two sentient species consciously decided to recognize the divide between the two biomes and remained separated. Aleen’s surface was dotted with the remnants of Aleena colossi, standing as relics of an ancient, technological society abandoned in favor of a simpler lifestyle.