I went up to Dawnstar to deliver some pieces of Mehrune's Razor to the museum and noticed this guy sitting on a boat just north of the museum. I am sure I have never seen him before. So I went up to talk to him and he offered to take me by boat to either Solitude or Windhelm, just like a carriage ride, only by boat. This is something new to Dawnguard, right?

I don't think so If im remeber I done it before.

Interesting... I have never seen him before - at least I don't remember him...

Next time you're in Solitude or Windhelm, check the docks area. The boat guys are new. They'll even take you to Castle Volkihar, but they'll charge 10 times the normal rate.
That place is "cursed" after all.

It is not!!! My friends live there!

Oh, as a side note, has anyone really tried to go there not being a vampire? I did and they called me a weak mortal, and said that I should get Serana to cure me at once.

Yes.
I find it's a nice little addition.

They only take you to the pier where you can take another boat to castle volkhair

Scenic boats mod for PC incoming.

But this is rather cool, especially for people who don't use fast travel.

I've broken into the castle a few times as a dawnguard by using the wooden plate whirlwind sprint method.

You can walk around inside the castle, talk to people, take stuff, whatever, no one is hostile.