HOLLYWOOD -- Some things are better left undisturbed.

That's the message behind the creepy new sci-fi thriller The Cave.

When biologists discover an underwater cave deep beneath the ruins of a 13th century abbey in Romania, they send in a team of cave divers.

They eagerly explore this new eco-system only to discover it belongs to someone or something else.

Cole Hauser, who plays the diving team's leader, says The Cave "blends elements of action adventure, science fiction, horror and drama. It's all of these genres rolled into one.

"It's like Alien, only set deep inside our own planet instead of in space."

Hauser, 30, is familiar with all these film genres.

He starred as the villain in 2 Fast 2 Furious, rode the range with Woody Harrelson in The Hi-Low Country, and went to war with Colin Farrell in Tigerland and with Bruce Willis in Hart's War and Tears of the Sun.

He learned to fight extraterrestrial monsters with Vin Diesel in Pitch Black and played a skinhead in the drama Skins.

Though there is a creature in The Cave, Hauser says it is "played more for suspense than shocks and screams. It's not as visible as the creature in Alien, or even in Pitch Black.

"I think it makes it really creepy when you only get glimpses of the creature rather than having it thrust in your face every few minutes."

The diving suits and costumes for The Cave were designed by Calgarian Wendy Partridge and created in her Calgary costume workshops.

Partridge also designed and created costumes for Hellboy, The Fantastic Four, Highlander: Endgame, Underworld and Blade II.

"At our first costume fittings ,we all realized they were very tight and form-fitting, so we knew we'd all have to start working out," recalls Hauser, who shares scares in The Cave with Piper Perabo, Eddie Cibrian, Morris Chestnut and Lena Headey.

Hauser admits he started working out by swimming, rock climbing, running and lifting weights.

"I was grateful I did because the tanks we wore without wetsuits weighed 95 pounds."

He says the underwater sequences were filmed partly in the Yucatan and partly in Romania, where the majority of The Cave was shot.

"Our stunt doubles, who are real cave divers, did diving in the Yucatan for some spectacular footage, but most of the actors' work was done in a tank they built especially for us in Romania."

The tank is so impressive that other productions have already signed to use it.

"The location managers for Underworld 2 were scouting our tank while we were using it and were scheduled to move in after we finished," says Hauser.

The creature in The Cave didn't faze British actress Lena Headey.

Before she encountered it, she'd battled werewolves, man-eating horses, haunted trees and mud creatures in Terry Gilliam's The Brothers Grimm.

"The Brothers Grimm is a work of fantasy by one of the true visionary filmmakers working today, whereas The Cave is just one big silly, scary action movie," says Headey, 28, whose films include Waterland, The Jungle Book, Mrs. Dalloway and Ripley's Game.

Just how silly was it for Headey?

"You're in a huge water tank all day chasing a man in tights with a monster's head," she explains.

What proved worse for Headey was filming in Romania.

"It's a country that has lost all its charm.

"It's the black hole of filming and we spent three months in the country.

"It's a cheap place to film, so Romania is getting tons of movies. Films were lining up behind us to use our locations."

As far as scary goes, making either The Brothers Grimm or The Cave can't compare to Headey's experience on her first film Waterland, when she played the younger version of Jeremy Irons' wife.

"I had to do a nude scene. I was just 18, so there I was, a teenager on my first film set, making out with an actor I didn't know in front of a bunch of crew people."

For The Brothers Grimm, Headey's character had to skin a rabbit while talking to Matt Damon and Heath Ledger.

"They actually wanted me to skin a real rabbit. I told the special-effects people if they could create a flying wolf, they could make a skinable bunny."

Next up for Headey is the romantic comedy Click with fellow Brits Matthew Goode and Darren Boyd.