Easily the tallest game level of its day, and definitely the most vertigo-inducing. The Security level is a massive vertical shaft leading from the main part of Citadel Station to the Bridge. Snipers were a real problem in the original, and knowing some people, could be here too. Watch yourself on some of those high areas, System Shock had no fall damage, but UT certainly does :).
This map can also be great fun with the Matrix Moves mutator.
Update: June 14, 2001
The map has been repackage with a mod conversion of the original music! If anyone feels like doing an even better conversion, please do!