Elven ruins secret unaccessible?

[Elidar]

Elven ruins secret unaccessible?

All right, so I found these elven ruins, marked with a "?" where the Nightwrath and several wraiths are protecting the treasure. Turns out those are quest ruins where you went with Keira in pursuit of Ciri.
On the map there are three "?". One of them is hidden treasure that's easily found, another is a place of power and yet another "?" that I can't determine. I believe the other two secret places are underground so I found a cave entrance in the side of a rock and went back exploring. Earlier part of the ruins is sealed of by a what seems to be a small avalanche, there's also an illusion (portal?) icon near it.
So... Did anyone figure out how to access those other nearby secret locations? U couldn't find a way to reach the place of power or the other place.
There's a picture of this palce in the attachement.

 

[PanKamien]

Sometimes you can find corridors that are covered with illusion, you need special artifact to dispel it.

 

[Elidar]

I have that artifact and I indeed found a corridor. However, that corridor didn't lead me anywhere. And there was no illusion showing near that avalance even though there was an icon on the mini map. So I am stuck pretty much. Perhaps it's just a bug or I am not attentive enoough and missing something.

 

[la_verne]

They might be underwater. Some are walls u need to break with aard. And a couple of illusion walls that needs an artifact to open. A certain witch gives this to u.