Glass can be found on the walls and floors of several stages - Urchin Underpass has both platforms and walls made of glass in its side alleys. It sees a minor use in some other stages, including Arowana Mall, Camp Triggerfish and Port Mackerel.
Glass also appears during the final stage of The Rampaging Octowhirl!, the third boss battle in Octo Valley. Some of the rotating floor is destroyed, making it harder for Agent 3 to get the Octowhirl caught in their Ink. It is also used in some other missions, such as Propeller Lift Fortress.
Some glass in the old version of Urchin Underpass.