The Great Hall is a unique location in Crash Bandicoot that can be visited during the end of your stay on Cortex Island. You can get there after completing The Lab level and before you start the final fight with Dr. Neo Cortex. In default, this level can be completed very quickly because the portal is right next to the starting place.
Of course, The Great Hall is not a location without any meaning. You can return here when you get Clear Gems that you get after completing a perfect run of a level. They are placed in special platforms on which you can jump (the picture above).
Getting all Gems allows you to reach the balcony where you can see the hidden ending during which you meet with Tawna. After watching it you can also see information about what happened to all bosses that you have defeated during the game.