Something horrifying is unimaginably frightening and disturbing. It can vary from anything including an unpleasant car crash or seeing someone break down into a savage rage. Horrifying things are likely to give you nightmares or potentially scar you for life. This word has a far stronger meaning than simply being scary or creepy.
The woman woke up to the horrifying sight of a rapist dangling the severed head of her baby with a sinister smile on his face.