Behind the door

At the top of the pyramid structure up to the control room, you open a door to find a large group of enemies to deal with, including a gold Elite. A second inner door only raises after several seconds. One challenge (you can probably think of others) is to kill everyone before the second door is up.

Gold Elite challenges

There are also challenges to be had with the gold Elite. For example, lead him back to an edge of the structure, and dodge at the last moment so he goes over. He doesn't seem bright enough to make his way back up. Needless to say, dodging that huge sword is not easy; but it's possible. For even more of a challenge, lead him all the way back down the zigzag path, and over to the crevice out in the snow. Dodge his final swipe so he falls in. And then just to rub it in, do your best impression of an Elite's "Ah hah hah hah!" business.

When he's chasing you down the path, you'll occasionally hear the hum of his blade as it just misses your ears, which is pretty scary. It's yet another amazing bit of detail from Bungie.