Board Thread:Legitimate Canon Questions/@comment-13895380-20170923035330/@comment-4091815-20171103200934

"basically without form" meaning it could be anywhere, it only manifested the spiders when it wanted to infect someone. The general feeling of overwhelming fear was pervasive throughout Beacon Hills as evidenced by the increase in violence against supernaturals.

As to the specific room that was generating the crippling sense of dread, Anuk-Ite apparently didn't want anyone casually wandering in there and left a little something behind to make it unlikely.