If you descend down the stairs in the thrall dugeon at Castle Volikhar and walk past the cages to the very end of the room where the rubble is, and take a left there is a giant sewer grate with rushing water under it which looks like one of the ones you can open. I was wondering if you could open it or if there were any other secret passages besides the undercroft? I only ask because Fort Dawnguard has that giant secret cave, so I would expect the other side of DG to have an equivalent.

I've never seen it so I don't know. I figured someone from the PC group would have found it at least. I'll have to look.

I always assumed it was a way for the Dawnguard to sneak in?

No Dawnguard I was with sneaked in, they just charged the main entrance. The grate looked interesting, but being a console player I could never do anything with it.

I'd be willing to bet members of the Dawnguard were supposed to sneak in through that and open the front gate from inside the castle. Sounds like cut content.

I mean, seriously. If you know the Dawnguard is coming, why not just close the front gate? A castle isn't much good if you can't lock the front door.

But immortal vampires who probably have had centuries to thousands of years of experience would never ever think to lock a door. Who the hell locks door when you know a group of hunters are trying to kill you. *Sarcasm

So they would somehow manage to get in there, get out of a grate I do not believe they could reach (I am too lazy to go and look), then sneak past all those super sensitive vampires to open the front door? They would be food before they got that far. It is just a grate, the vampires probably sweep the rubbish down there if they ever clean up. Would be nice if one of the PC players checked it out though.

And vampires are hardly going to lock the front door against food that wants to come calling. They were arrogant enough to think the Dawnguard were no threat, and rushed out the door all hungry ready for a feast.

If that were the case, then a secluded castle filled with thralls to feed on would be unnecessary. And remember that there WAS a gate when you first arrived at the castle. It makes sense for the Dawnguard to launch a sneak attack on the vampires when the enemy theoretically has the upper hand in terms of terrain. And despite what one may think, those vampires are easy to sneak past.

I always assumed that's where the thralls/cattle did their...uh... necessities.

What Dawnguard would be crazy enough about killing vampires to dive in that filth to sneak in?!
Well... not counting Isran!

Funny story. There was a siege on a castle in medieval times that was achieved that exact way. The castle actually had toilets, with chutes leading to the outside. Some dude got the brilliant idea to lay siege to it by pulling a reverse Shawshank Redemption and climbed UP the poop chute and into the castle during the dead of night. He then opened the main gates and his buddies laid siege to the place. Talk about a dirty job...