Toronto’s annual Contact Photography Festival kicked off on May 1 with a variety of public installations, including images of the city’s underground waterways that were showcased, appropriately enough, in Toronto Transit Commission (TTC) subway stations.

The festival, which runs throughout May each year, has often seen artists use out-of-home (OOH) advertising media—including billboards, wall murals and transit posters—in new and creative ways. For this year’s subway exhibit, Contacting Toronto: Under This Ground, the work of Michael Cook (example pictured) and Andrew Emond has exposed previously concealed waterway spaces to the public for the first time at a large scale, visible to more than one million daily commuters.

“Toronto’s subway platforms are the perfect location for this project, allowing viewers to reflect on a layer of the city to which we are all connected, yet rarely have the opportunity to see,” says Sharon Switzer, arts programmer and curator for Pattison Onestop, which manages OOH media for the TTC.

Cook’s still photos have taken over 45 posters in St. Patrick Station, while Emond’s stop-motion animated depictions of Toronto tunnels are playing on the TTC’s digital signage network.