Okay, I've been struggling with the exact same issue for a couple weeks. I have not had trouble with the sewers, but all exits from hydlaa are bugged. Really annoying....

I've been working with Caarries advice for Mac OS X fixes. I used the repair updater and downloaded some files. I have the crash log for when I try to enter the game with the crashing character... There's a whole bunch of yellow text, but the most interesting is the fatal error at the end:

crystalspace.maploader.parse.texture:
  Could not load texture 'dirt01.dds', using checkerboard instead
  [node: world,textures,texture(name=dirt01.dds)]
(0) : fatal error C9999: *** exception during compilation ***
Cg compiler terminated due to fatal error(0) : fatal error C9999: *** exception during compilation ***

As per Jonnikhan's last post, portals have not helped me with the problem. All new characters have the same problem.


Update: The downsampling fix has definitely helped! I'm going to run around a bit and see what happens.


Alright, hope to hear some good help!
Aceri