A little thing I noticed.

I still don't understand: if it was really just a background object like some people are assuming (and even I would), then why that red beam?

This is really mysterious. Some things make me believe that it actually is El Nath castle (the top part), but there are some things which aren't really the same. For example, it apparently is missing of one of the right base pillars.

Better quality comparison:

 Spoiler

It's really, really similar, though. But then again, it could've just been an object they used for the video, IF there wasn't that red beam which drawed many people's attention on it. Looks like that could be where the Black Magician (or his forces) is.

EDIT: Watching the video again made me change my mind. I'm now 99,99% sure that it IS El Nath's castle. Even if the base pillars aren't EXACTLY the same, the rest of it totally looks like that one.

red beam? it's blue. it's really, really, really blue.

the picture from the big bang video is flipped, it's looking at it from the opposite side as nath, which lends more credence to it being from the victoria island side. if you look, the two side pillar lengths are left short, right tall on the nath picture and left tall, right short on the video picture. it's the exact same castle without a doubt, just from the opposite PoV.