There's a direct link there too ... and maybe your Mac doesn't interpret the CGZ extension for belonging to either Cube or AssaultCube ... but it should work perfectly if you place the file into packages/maps.

Regarding the map - the screenshot looks really good,
and you've put a lot of work into detailing in quite a few parts of the map,
the lighting is also pretty good in most parts of the map;
maybe the red lighting is a little too red and the tunnels a little too dark though;
I know the flickering I get with all of the bridge mapmodels can't always be totally removed - it's just a driver/opengl issue that's a legacy from Cube :-P
But ... try rotating your mapmodels to true multiples of 90 ... 180, 270, 360 - all the models I inspected had fractional degrees - bad idea!
The only time I really wanted to ignore your mapmessage "do not edit this map" was when I was somewhere on one of those grassy bits ... there's a step there I have to jump up on ... and I don't think that's really a good thing there, maybe change that.

Oh - particularly enjoyed the ammo box "swimming" in the nicely coloured water.
All in all a pretty good job.

Oh, sorry, I see now I wrote it very misleading.
I didn't actually mean every model ... of course stuff like barrels or palettes don't need to be 90° degree aligned ... I was merely talking about all bridge-models ;-)