This real-life adventure is not for the faint of heart.

Greg McLean has trained his fans to expect the worst from his films.

Think what Mick Taylor did to those poor travelers in “Wolf Creek.” Or how the beast in “Rogue” made mincemeat out of tourists in that 2007 gem.

The director’s “Jungle” strips away his signature trappings. Yes, the characters face one nightmare after another deep in the Amazon. And there’s a grossout scene that shouldn’t shock anyone familiar with the “Wolf Creek” franchise.

It’s all based on a true story, a wrinkle that could have handcuffed the director given his zest for outlandish thrills.

“Jungle,” in theaters and On Demand/Digital HD Oct. 20, shows he’s more than a grindhouse devotee.

Daniel Radcliffe stars as Yossi, a young Israeli stricken with wanderlust. He disappointed his father by heading to Peru, where he hopes to leave his staid life behind.

He quickly bonds with two new friends with a similar zest for travel. Yossi’s curiosities get the better of him when he meets Karl (Thomas Kretschmann) during a stop in Bolivia. Karl tempts Yossi about an adventure he won’t find on any map.

Yossi convinces new buds Kevin (Alex Russell) and Marcus (Joel Jackson) to join him and Karl on what could be the trip of a lifetime.

It won’t be easy, and they know it. What they can’t predict is how their disparate personalities will challenge them as much as the titular jungle.

You can easily divide “Jungle” up into two distinct stories. The first, alas, is superior to the second. Getting to know Yossi and pals is a fascinating glimpse at the youthful mind. Why would anyone trade their creature comforts for long, exhausting treks in the jungle? Think of the bugs, the horrible food and the drenching rains?

The screenplay, credited to Justin Monjo based on Yossi Ghinsberg’s best-selling memoir, reveals why all of above can be irresistible. We’re also privy to their modest, but significant, personality divisions. Bonds form quickly.

So do levels of distrust.

Which makes the film’s second half a modest letdown. We’re in survival mode, and McLean captures the Amazonian jungle with a keen eye toward its beauty and menace. Yet those character dynamics give way to simply staying alive. The latter should be just as captivating. It isn’t.

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Radcliffe keeps his Israeli accent consistent throughout, no small feat. He’s crafted a post-“Harry Potter” career to be admired, making us forget about that boy wizard with every new role.

“Jungle” is no different.

Russell and Jackson offer stable support, and Kretschmann delivers a wild card performance the screenplay demands. We still want more of Karl and the disagreements that break out when the going gets rough.

McLean’s Mick Taylor villain will return in a new season of “Wolf Creek,” and the director says a third film isn’t out of the question.

Sometimes the scariest stories don’t involve charismatic killers but Mother Nature bearing her fangs. “Jungle” proves it.

HiT or Miss: Fans of Greg McLean’s horror outings may be surprised by ‘Jungle,’ a thriller showcasing the director’s strengths in a whole new setting.