Right click the Main toolbar > Choose Layers from the pop-up menu.

The Layers toolbar lets you interact with files imported from Autodesk VIZ, which use Layers to organize geometry.
The Layers toolbar provides the following controls:
This toolbar is available from the Customize Display Right-Click menu.
Web Designer - offers freelance web design services, redesign, graphic design, content
management, web development and e-commerce.
LTD