Can the huge gate to the far right be opened or is it a red herring? You get an achievement for getting down there, but that seems to be it. I played through the game going the other way, but that still bugs me.

I beat the game last week and I have no idea what you're talking about 
 
You should provide a walkthrough video and specify the time mark. Also, add a spoiler warning somewhere

It's where you get the Achievement "Alone in the Dark - beneath the arthropod".

That's the "secret" extra bit they put in the PS3 and PC versions. It opens after you get all of the eggs. It's mentioned on the page, too.

That being said, screw that place. It's a bunch of running around in pitch black, relying only on sound to not die.

Thanks, I guess I am not going to bother then.