Double the fun of a window perch. The Kitty Sill - Double Stack EZ Window Mount by K&H is the perfect window-mounted play/sleep area. Incorporating steel frames and our unique push’ n ’turn super strong suction cups, this window-mounted gem is sure to please. As with the single unit, it can be folded up against the glass in seconds to allow for normal operation of blinds, curtains, or shades. Covers easily remove for washing. One-year limited warranty. The second level hole allows movement between levels. From the manufacturer: At K&H we know how much you care about your pets. That's why with over 20 years of experience, we design innovative, quality products to make their live better.