The cake is a reward promised by GLaDOS to test subjects to encourage them to complete the test chambers. It's existence has been questioned by many subjects including a scientist called Doug Rattmann who warned Chell about GLaDOS and claimed that "The cake is a lie". Despite this the cake actually does exist but is hidden within a secret room in Aperture Science where shelves full of artificial intelligence spheres look on.
After the heroes rebuild X-PO, he tells them to search for the Foundation Elements but has no knowledge of any available elements to search for first. X-PO states that the cake is known to all A.I constructs and suggests that it might be a Foundation element. The trio head to Aperture Science to recover the cake but end up getting trapped within the Enrichment centre. Wheatley attempts to help them escape but is unsuccessful, eventually GLaDOS gets fed up with Batman, Gandalf and Wyldstyle "breaking the rules", as she states, and attacks them. After failing to defeat them she locks them in an oven under her chamber where the cake is hidden where the heroes finally collect the cake and retreat to Vorton.
- X-PO describes the cake as "delicious and moist". These are the exact same words GLaDOS uses to describe the cake in the credits song "Still alive".
- The Cake is a Black Forest cake.