Gates that cant be closed? Options

[Elendil]

*****Possible Spoiler*****






I'm on the main quest, closing gates to get forces sent to Bruma. I've closed Kvatch, Chorrol, Cheydinhal, Bruma and Skingrad. I then went down to Anvil, but NOOO... There are 3 towers, 2 that just houses a Corpse Crusher and not much else, and then the main tower on top of a mound or hill or whatever you wanna call it, but there is NO ENTRY POINT!

I came across one exactly like like this before out in the middle of nowhere. Is it possible that some gates are not possible to close until you finish the main quest? Or am I missing something?