There are separate entrances for men and women because you have to go through a dressing room. I was wearing a long-sleeved tunic over pants and I had a scarf, so once I'd covered my hair I was dressed appropriately, but there were racks of blue and mauve abayas with hoods for women whose arms or legs were bare, or who didn't have a headscarf.
Men don't have to cover their heads but shorts and tank tops aren't allowed so there are robes available for them to wear if needed as well.
There are racks outside the main prayer hall for shoes, and this is where there's a logjam. Once you're inside, the space swallows you up, and there's no sense of a crowd.