Citadel
Overview
History
Soon after GoldenEye was released data miners found the strings "Citadel" and "CITADEL" buried in the game's data alongside strings for the other levels. This prompted speculation about a hidden level and players asked Rare for answers. Rare responded on the Rare Rumour Mill, a page of the official Rare website in 1998.
Q: What's all this about a hidden 'Citadel' level?
A: 'Citadel' was a very rough test level designed during the early stages of multiplayer mode. It's not in the finished game in any shape or form, and Oddjob and Mayday wouldn't be in it if it was.
— Anonymous GoldenEye developer