The Mill worked closely with Guardian’s dedicated VR team to create the content for Underworld by laying out the virtual sewer structure using data and footage taken from the Victorian sewer system. The experience allows the user to step into the shoes of an urban explorer and discover the hidden labyrinth of London's Underworld - a subterranean web of Victorian sewers and lost waterways that lie active, deep beneath one of the world's most famous cities.

Guided by urban explorer and geographer Bradley Garrett Underworld begins in one of London’s lost waterways, the old river Fleet, in the blood sewers under Smithfield meat market and continues down to the floodgates of the River Thames. At a fork in the tunnels, viewers can choose their own pathway - one takes them on a journey with Will Self to explore the mythological allure of the underworld as a place for the dead and another features the story of the flushers - the people who work in the sewers.

Mill Creative Director Adam Grint comments, ‘Most people initially give me a slightly confused look when I explain that for the last few months we’ve been making a VR experience about exploring London’s sewer system. Furrowed brows relax slightly when I describe the unseen world that lies just a few feet beneath our feet, a world that sustains us every day.

This experience peels back the layers and allows us to explore for ourselves - a “city within a city". It’s a word of surprising beauty, each brick hand-laid, and a staggering example of the ingenuity of Victorian engineering which literally saved thousands of lives. Working in conjunction with the Guardian has given this project the journalistic integrity and accuracy required for this to be a true representation of being down there for real.

This is all allied with the breakthrough VR platform that is Google’s Daydream which has allowed us to bring new levels of interactivity to a VR experience on a mobile device.’

Underworld is the first project in a series of six editorially independent virtual reality films which the Guardian will launch on Daydream over the course of the next 18 months. A new interactive Daydream film and 360 video will be released every quarter.

Working closely with both the Guardian and Google, The Mill’s Product Development Team created the platform on which to host and launch the new Underworld experience, Google Daydream’. The task was to design a system that would host and showcase unique VR experiences, fully interactive in real-time whilst ensuring the highest quality visuals were maintained throughout.

The Mill’s Lead Creative Technologist Kevin Young explains, ‘Working with the Guardian’s VR team, we strove not only to tell a new compelling story set in the century old tunnels beneath our very own backyard, but also to design an intuitive and robust delivery system that will also bring future stories from the Guardian to Daydream.

Designing for a new platform is not without its challenges. The team at Google were very helpful in giving us guidance on their new hardware and we worked hard to take advantage of the power and unique features of the then unreleased Daydream devices. Underworld started with prototyping ways in which the user could walk down the tunnels; we really wanted the user to feel what it’s like to be in the shoes of an urban explorer, to have that sense of discovery as you traverse. Once we’d decided on a control system we built the experience around the extents of the controls balancing the walking speed with points of interest and the narrative audio from Bradley Garrett.

Finally integrating models from the Mill’s 3D Team and environmental audio design from the studio Mixed Immersion brought the experience to life.’

A re-imagined version of the first collaborative, multi-award winning VR project between The Mill and the Guardian, ‘6x9’, will also be on Daydream, allowing users to walk around the 6x9 cell to experience solitary confinement whilst being able to physically move around the cell.