"Vertigo Tower Addon" adds a Sunset and a Storm HDRI/Skysphere to the "Easy Environments: Vertigo Tower" set.For owners of the main set, it includes full scene preloads as well as separate HDRI/Skysphere preloads.Customers who do not own the main set can still use the HDRI (Iray) and Skysphere (3Delight) preloads, e.g. for aerial renders.