Hi. So I got a quest from this gate keeper:

When I get inside, instead of an X this mark appears:

I already went to that spot, killed a bunch of those rat looking things and that wasn't it. I don't know what is the thing i have to get/kill or why is that mark there instead of the regular X.

Can anyone help me? Sorry if I am posting in the wrong section ^^".
EDIT: Noticed now that it is in the wrong section, but i can't delete this post so if a moderator could please move it to the right section it would be great, thanks and sorry. ^^