
It is so scary you need to sign a waiver.

The 17th Door in Tustin, California, is being hailed as the most petrifying haunted house in the world.

With 17 rooms - each more intense than the last - visitors are given one piece of advice: to escape shout 'mercy'.

After signing the waiver, you descend into the twisted mind of a university student, Paula, as her past comes back to torment her.

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Pushing the limits? The 17th Door in Tustin, California, is being hailed as the most petrifying haunted house in the world

With 17 rooms - each more intense than the last - visitors are given one piece of advice: to escape shout 'mercy'

After signing the waiver, you descend into the twisted mind of a university student, Paula, as her past comes back to torment her

She grapples with drugs, anorexia, and suicide.

The grotesque monsters appear in classrooms, the library, the cafeteria, and other seemingly familiar spaces. And they are free to touch and lick you.

Visitors are locked in each room at the fictional medical college of Gluttire for about 90 seconds at a time until a school bell rings and they move to the next, scarier experience.

The experience is the brainchild of married couple Robbie and Heather Luther, who have poured more than $100,000 into the project.

Even horror enthusiasts say 17th Door is one of the most visceral experiences open to the public.

The grotesque monsters appear in classrooms, the library, and other seemingly familiar spaces. They are free to touch and lick you

Visitors are locked in each room at the fictional medical college of Gluttire for about 90 seconds at a time until a school bell rings

The experience is the brainchild of married couple Robbie and Heather Luther, who have poured more than $100,000 into the project

'Tame': Originally, they planned to make it even scarier - so scary that it would spark protests and be forced to shut down

Since opening on September 25, about a quarter of their hundreds of guests have screamed 'mercy' before the experience was over

Incredibly popular: The couple expect hundreds of bookings as Halloween approaches in the next two weeks

But Robbie, 36, insists it is far more tame than he had originally intended.

'My original plan was to do a haunted house so extreme and awesome that it would get protested by all these groups and then I would get shut down,' he told the LA Times.

'Some of my original ideas were pretty far out.'

But as it stands, it is already too much for many visitors.