Xeen's cronicles (Volume 2)

[RetroGamerUK]

There are a lot of secrets. Return to the entrance and examine everything carefully.

I assume you mean the entrance to the bastion?
I'd already checked every wall inside and out, checked again.
As you enter there's a torch in a holder, at the end of the corridor there's a stone demon head in the wall.
Checked every inch, couldn't find any switches or fake / destroyable walls.

I also checked outside again around the entrance, nothing.