Citadel is a faithful remake of the original game System Shock created in 1994 by Looking Glass Studios.
If you've never used the 3D modelling package Blender, download it. Open the .blend file in this download, and use Shift+F to enable fly-thru mode with WASD in the blender 3D viewport (Tip: Hold shift to fly faster). You can also hold down the middle mouse button to rotate view. Enjoy seeing the entire space station in all its pre-alpha glory! Disclaimer: Work-in-process files are not necessarily indicative of final game. All content subject to change at discretion of the Citadel team.
Was this exported from a darkplaces map?
Yes. It was a bit tricky, had to use 2 converters.