For the rest of the year, Universal Studios is a family-friendly theme park with rides and attractions based on Hollywood blockbuster movies such as Shrek, Men in Black and ET. Some are "4-D" films in which 3-D footage is brought to life with moving seats, surprise air blasts and water squirts, while even the park's extreme attractions like The Mummy in-the-dark rollercoaster look tame compared with Halloween Horror Nights.

As night falls (6.30pm-2am, until October 31), the park closes and while families head home, a 1,000-strong cast of scare-actors takes its place to frighten Horror Nights fans who have been flocking to the annual fright-fest for the past 16 years. To celebrate this milestone in Halloween history, Universal is staging a special "Sweet 16" super-charged event, including the return of all its most terrifying characters from previous Horror Nights. So, if you enjoy being frightened, it's the year to be here.

Walking back into the park after dark, it is barely recognisable as the fun-filled studio backlot from earlier in the day. Special effects lighting sets the scene, background music is replaced by ghoulish howling and the streets billow with thick fog. Uniformed guards at the entrance use loudspeakers to warn that you are entering an unsecured zone and that you do so at your own risk.

All good fun so far but when a maniac rushes through the mist to brandish a screeching chainsaw a few centimetres from your face - so close that you can smell the petrol - the adrenalin begins to pump, big time. Brace yourself, though, because the chainsaw lunatic is one of an entire gang that roams the park. And that's just the opening act.

No matter what frightens you, Horror Nights has it covered. Lurching through the smoke you may find zombies, vampires, ghosts, skeletons, scarecrows, goblins, psychos and clowns. And in the dark, you can never be sure whether the person next to you is a fellow punter or a character about to turn and scream through a decaying face.

The air is thick with screams of terror, though the shocks are expertly timed to avoid excessive intensity. On a walk through any of the three designated Scare Zones, you also hear much nervous laughter. And when you're not screaming yourself, try to spot the park's sly Halloween touches, like the neon sign for Mel's Drive-In diner that is doctored to read Mel's Die-In.

What really pull in the masses are the infamous Haunted Houses. A full year in the planning, seven such constructions are scattered around the park and these are where the scares get serious. Each house is an elaborate walk-through set based on a different theme - designed, constructed and lit for maximum shock value.

For example, Scream House Resurrection is a gothic mortuary built to look like a haunted southern-style mansion. Rooms are decorated with an incredible attention to detail and synthetic odours are even used to make each scene seem eerily real. This raises the level of tension and allows for even bigger shocks when scare-actors jump out of hidden doorways and through dummy walls - frequently reducing grown men to cowering wrecks.

Once you've entered the house, there is no turning back. No matter how frightened you may be to reach out and part the blood-spattered plastic sheets and make your way through a mortuary in which the dissected bodies are still half alive, you have to press on. Closing your eyes or hiding in the corner doesn't help either - because you have to get out somehow.

Most terrifying of all is an asylum in which the inmates have taken control. The lighting is reduced to a harsh infrequent strobe and one of the rooms is filled with hanging mattresses that you must push your way through. The flashing light allows masked inmates to appear and disappear behind each turn of the maze. It's the disorientating stuff of nightmares and fans happily pay $59.95 each for the privilege.

For your money, you also get all the usual Universal Studios rides and attractions, a pyrotechnic and projection display, plus a surprisingly-funny live cabaret show - Bill and Ted's Excellent Halloween Adventure - clearly a big draw with the locals.

As with most fears, familiarity is an great cure. After a few hours, the park feels less threatening and I discover the next day that the chainsaws are chainless and some of the scare-actors have normal day jobs, including a lawyer, a doctor and a teacher. They simply enjoy frightening the life out of people in their spare time, which in itself is a scary thought.

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