The hidden level 'citadel' has finally been found (goldeneye - nintendo 64)! if anyone has an action replay the codes are
8002A8F7 0029
8104468A 8970
81044690 3F44
81044692 BDEA
81044694 3F80
81044696 0000
81044698 4219
8104469A D89D
80069f80 00C4
check this site out first (the guy who found it explains what to do etc) Enjoy!!
Citadel information