The Deep House

 Alexandre Bustillo and Julien Maury enjoyed some infamy as part of the New French Extremity Horror wave of the late 00's with Inside, one of the better and most unsettling films of that short-lived movement. They've been plugging away since, with uneven results, and after some bad experiences working abroad they've elected to stay in France.

 In 2019 they released The Deep House, an excellent slow burn horror film that is low on explanation or common sense, but compensates by having a kick-ass premise, a bunch of great scares, great cinematography, and being creepy as all hell.

 Ben (James Jagger) and Tina (Camille Rowe) are a couple of twenty somethings trying to make a living by going into supposedly haunted buildings and filming their exploits. Ben is extremely British and very, very dickish, while his French fiancé is the more susceptible, easily scared one.

 Early on in the movie, they catch wind of a whole town that was submerged with the construction of a new dam, and decide that it would make a great webcast. So off they go to the south of France, equipped with SCUBA gear and an underwater drone.
 When they arrive, though, they find out that the lake is full of tourists, and that the town was demolished (as, sadly, they usually are in these cases; that's why there are so few subaquatic urban exploration pictures of this sort out there.)

 As (bad) luck would have it, though, a creepy local offers to take them to a branch of the lake that's off the beaten path, where he says they'll find a fully preserved manor house. Our intrepid youtubers take him on as a guide, and after a short dive find that he was telling the truth.

 The second and third acts are completely underwater, and the cinematography is astounding for a relatively low-budget euro-horror movie like this. The film plays very similarly to the same directors' earlier Livide (still their best, by my reckoning), with the young couple exploring the house room by room and finding evidence that things are very fucked up indeed in the house, with an expert buildup of creepiness that's not helped at all by their diminishing oxygen reserves.

 Things don't make an awful lot of sense, some of it by design (the movie subscribes to the idea that horror works best when it's unexplainable) and some of it due to weird decisions like recurring references to Tina's ophidiophobia. But it's an excellent update to the haunted house genre, with the killer twist that its victims are all divers.