It was the levels that occurred in the Derelict ("Boneship") in between the main levels, where you circled around a massive pillar with doors on the side where there were enemies and gear inside. The final one of the these levels featured the Space Jockey in the middle. I was always entranced by the atmosphere; the perpetual spiral downward in a land of bone, with nothing but black above you, and that eerie music playing. The main levels were always cool, with acid walls, doors that seemed to melt away, and human hosts fused into the biotechnology. The whole Boneship area is one of the most well-done settings for any AVP game I have ever played.