The Tunnel

 In 2007 the Australian government decided to tap into huge reservoirs of water that had filtered through to the abandoned tunnels beneath Sydney. The move gained some notoriety thanks to worries about a transient population of homeless people living underground, but it all came to nothing - the project was suddenly swept under the rug, quietly cancelled.

 That's the fictional basis for The Tunnel, an Australian found footage film that follows a film crew that tries to find out what the story was behind the sudden, mysterious death of the controversial water-recycling project. After being stonewalled by the government, journalist Natasha Warner illegally leads a small news crew into the tunnels into the darkness beneath. Where, of course, they are stalked and picked off one by one by... something.

 The film is framed as a documentary looking into what happened in this expedition, alternating between talking head interviews, the footage they shot both before and during their doomed underground jaunt, and incidental footage from security cameras. There's a surprising amount of buildup, which goes into the office politics at the newsroom and informs the inevitable character conflict when things go wrong later; The film's premise also gives a credible justification for everything being on film (although that gets a little contrived late in the game) and it allows the movie to look a little better than it would were if it were just people waving cameras around. You get footage of the film discussing how to get interstitials and pickup shots, and you also get to see it as well, which is rather clever.

 The acting is also fairly good, and the characters are simple but well-developed. The technical crew (Steve Miller and Luke Arnold) are a pair of knuckleheads who have a very credible dynamic, and their producer (Andy Rodoreda) is pretty good as the one trying to hold things together.
 It's interesting that while the film makes it perfectly clear that Warner's carelessness is 100% responsible for the crew's dire straits (and a couple of deaths), she still comes off as sympathetic thanks to a near-constant stream of casual chauvinist comments from the people that are supposed to be supporting her.

 There's a lot of running around in dark tunnels, of course, and lots of murky scenes shot with night vision cameras. Director Carlo Ledesma doesn't find a way to make all the scrambled footage cinematic, but a good ambiance, some grisly findings, a very clever "oh shit, we're being watched" moment and a couple of well-placed jump scares keep the tensions running high.
 All the darkness also keeps whatever lurks in The Tunnel nice and mysterious. It's a gamble made necessary by the film's very low budget, but it works beautifully here; The few glimpses we get of it are extremely effective. The director and Writers/producers/editors Julian Harvey and Enzo Tedeschi do a good job of leaning into their limitations.

 The Tunnel seems almost forgotten these days - seemingly eclipsed by As Above So Below, which came a couple of years later and is inferior to this one in most ways that count. It's a very solid entry into the found footage horror pile.