World's Deepest Marathon

Set in Sweden's Garpenberg mine, The World's Deepest Marathon follows 55 runners attempting a full 42.2-kilometre marathon in one of the most extreme environments on Earth: relentless heat, high humidity, darkness, narrow tunnels and a physically demanding 2.4-kilometre loop.

Alongside the runners, the film explores the technology, people and systems shaping the future of modern mining. The result is a character-led documentary about endurance, human potential and the willingness to redefine what is possible.

The sound challenge

The mine needed to feel vast, physical and alive without overwhelming the runners' stories. The mix balanced authentic location recordings with breathing, footsteps, movement, voices and machinery, moving between:

• The mine's scale and pressure
• The runners' physical strain
• Moments of calm and tension
• The emotional weight of personal testimony
• The energy of the race's key moments

The challenge was knowing when to build the sound and when to strip it back.

The approach

Using the production recordings, music and designed effects, we shaped the film around several deliberate moves:

• Adding subtle wind to keep the underground environment present
• Protecting dialogue where music was masking key lines
• Fading music away during the descent to foreground voices and mechanical sound
• Reducing the score to create a more immediate, diegetic feel
• Stripping back music and effects beneath the film's more poignant voiceover
• Reducing "epic" musical weight when it competed with emotional dialogue

The most effective choice was often subtraction: removing music, reducing effects and creating enough space for a voice, a breath or a footstep to carry the scene.