A way into Ice Witch's castle?

There is a door which can not be opened and a deactivated pentagram.
Just a sign that tells about a service entrance at the rear. But there I can only find moles to kill and some shelves...

What/where is the secret?

Talk to the innkeeper nearby. If your persuade is high enough, a pentacle will appear near a door into the Ice Witch's castle.

Thanks a bunch, my persuade skill of 120 hasn't been high enough.

I've been enchanting a ring with +100 persuade and talked to her again using it.
She activated the pentacle, and - the funny thing - her last sentence was: "'I'd just like to kiss your ring." - like if she knew what my problem was.