A scene from "Diving Into the Unknown"

Juan Reina didn’t know if he’d ever go back to Purdalen, Norway. It was February 2014 and while he was working on the documentary “Diving Into the Unknown,” the filmmaker had found an entirely different meaning in the title than when he first started rolling the camera in 2010 when Jari Huotarinen and Jari Uusimaki, a pair of Finnish divers that were part of a team attempting to set a world record by reaching the depths of the underwater cave system in the small Norwegian village, died while navigating the narrow passageways and chilling water at 130 meters below sea level. Neither Reina nor the surviving divers on the team — Patrik Gronqvist, Vesa Rantanen, and Kai Kankanen — had any desire to return, all of their careers put on hold as they struggled to come to terms with what went wrong, and yet conscience called on Gronqvist, Rantanen, and Kankanen to retrieve the bodies of their brothers in sport. That, in turn, led to a call to Reina to resume filming, not necessarily for the purpose of a movie, but as a document retracing what happened for the official record. However, in creating a document for the local authorities, the team would have to defy them for a time since shortly after the tragic accident, Norwegian police made it illegal to access the cave. Still, they took their chances, and in the process found they had some unexpected allies in the community.

“This cave is in such a remote location, surrounded by mountains [that] you don’t even get a phone signal there, so the authorities didn’t know we were there,” Reina confides, shortly before the film’s North American premiere recently at the DOC NYC Fest. “I’m pretty sure that many of the villagers knew [what was going on] because you can imagine five or six big vans with Finnish plates coming there, but they all knew how important this is, not only to the families of these divers and to his friends, but to the whole community there in Norway, that these bodies can be taken back to Finland.”

While Reina set out to capture the exhilaration of reaching parts of the earth that few, if any, humans ever had before, he wound up doing one better in “Diving into the Unknown,” by observing how the divers push their limits emotionally as well as physically, turning tragedy into a modicum of triumph as Gronqvist, Rantanen, and Kankanen brave the same treacherous conditions that ensnared Huotarinen and Uusimaki to give them the dignity of a proper burial. The aquatic footage is breathtaking, but Reina is more likely to draw gasps above water where the divers’ determination, care and concern for one another to pull off the seemingly impossible is tremendously moving. While in New York, the director spoke about returning to a film he didn’t know that he’d ever finish and how the production shifted, as well as the type of equipment used to shoot the film and how he made the film feel completely in the moment through the sit-down interviews he conducts with the divers.

A scene from "Diving Into the Unknown"How did this film come about?

We actually started quite a few years ago – in 2010, two cave divers wrote a book about a cave system underneath Budapest in Hungary and they approached us. I was fascinated by these guys and when I started meeting these different cave divers, I realized these are true explorers of modern times, so I was really fascinated by what these guys are doing and we thought this would actually be a great documentary miniseries/documentary series, [though] even in the beginning, we had it in mind we could do a feature-length documentary out of the footage that we have.

When we met the leading characters [of the film] in 2012, they wanted to break a world record in underwater cave-diving in Spain and it made more sense as a feature [since] I thought [the world record attempt] could form the [through] line of the story, but I wanted to explore this unique friendship that these guys have between them [and how] they are very close with other cave diving groups around the world.

Sadly, of course, two of the divers die – how did that change the trajectory of the film?

That obviously turned the whole project upside down. The dive in Norway was partly a training dive for the world record dive, but mainly they wanted to film the access between the two entrances to the cave system and then this terrible accident happened. We thought [the film] was dead and we put it aside – we thought we can’t continue any further with this. And the three survivors all said they might even just quit cave diving. But then the whole thing changed when the official operation [to retrieve the deceased divers’ bodies] was aborted, so that was a big change, so the survivors said, “We can’t leave the bodies there. We must get them back up no matter what.” So that changed things quite a bit.

A scene from "Diving Into the Unknown"Who approached who to resume filming?

We knew each other for a few years already – like what happens many times in documentary filmmaking, you become friends with the main characters, so when they made the decision to go back there to retrieve their friends, I’m sure they had talks before they contacted us about it, but they started communicating with us when they made the decision. It was never in a way that they called us and asked us to come along, but after quite a few talks, we all decided that because this is such a unique event, and they wanted to film all the underwater stuff for the Norwegian police, so we provided the cameras. During that process, we just said, “Let’s film everything and decide afterwards what to do with the material” because there was this trust already. Even the funders, they didn’t know we were going there, so we just had to keep everything within this little close circle of friends.

One of the first things mentioned by one of the divers is how the technology can’t reach the caves, so how did you figure out how to shoot this?

[One of the] writers of the book is dedicated to underwater filming, so we knew he would be able to operate the camera in certain depths of the cave and beyond that, we just had these special GoPros with underwater cases, so that’s how we managed to get to the deepest points of the cave. We knew that the GoPros can last for two hours more or less but at the same time, when they do these long dives, most of the time [the divers] are just decompressing the pressure off from their bodies, so we started filming when they started the mission and then carried on filming until the battery ran out or the [memory] card [filled up].

A scene from "Diving Into the Unknown"You really convey a good sense of the topography and geography for the caves to orient the viewers. Was it challenging to relay that information?

It was extremely challenging [since] we are talking about a sport which is very technical and very foreign to most of us. [The story] has a lot of different turning points and on top of this, we have four main characters, and both visually and the way it sounds, we really wanted to convey the story in a way that the audience would feel like one of the divers, so the underwater footage is more from the characters’ point of view, and I wanted to reflect that feeling in the graphics, which is why we decided to use 3D animation, or the music or when we were filming outside on the surface.

At what point did you decide to do the sit-down interviews?

We interviewed them before the mission and after, but all the interviews were done in exactly the same location because I really wanted to have the feeling of present time, so I didn’t want to have an interview shot from a totally different location suddenly popping out [where] the audience would start asking, okay, what was this?

Some filmmakers use voiceover in a way that they either script it or they interview [the subjects] after something has happened, so then it’s all just remembering, but what we did was [we mixed the interviews from] before the mission where they’re describing their fears or worries or expectations [with], for example, the footage just as they’re getting ready for the first dive, and it’s a totally different feeling. I wanted to have the story really takes [the audience] along and they would feel like okay, what I’m looking now at the present.

A scene from "Diving Into the Unknown"It really does feel immediate. What’s it been like traveling with the film?

It’s been shown all over the world and yes, I can now see how, no matter your cultural background or nationality, your age or whether you’re a woman or a man, this brotherhood [of divers] is really affecting people. It’s been quite remarkable to see and this was my aim in the first place because I’m not a diver myself, but [I wanted to show] how physically and mentally demanding it is. Even outside of the mission, in order to do cave diving at such an [accomplished] level, you have to be a person really who can put your emotions aside so you can really go through this. These guys are there for hours and hours underwater in ice cold water and it’s pitch black and anything can go wrong, so it really demands a lot.

“Diving Into the Unknown” does not yet have U.S. distribution.