Metrolinx is sharing a rare look inside the record-breaking tunnel currently being carved out for the 7.8-kilometre Scarborough Subway Extension (SSE) project.

This costly and controversial three-stop extension for the TTC's Line 2 Bloor-Danforth will run in a single bidirectional tunnel, unlike the twin-tunnel construction used for other extensions and new lines built in recent years.

This single 10.7-metre diameter tunnel — wide enough to house a three-storey building — will be the largest subway tunnel in Canada once complete, and its immense scale is apparent in a new photo released by the transit agency on Wednesday.

I spy with my little eye... someone safe!

Safety is central to everything we do on the Scarborough Subway Extension, which is why this crew member (can you spot them?) is always wearing their Personal Protective Equipment (PPE) on the job site.#ScarbTO #torontotransit pic.twitter.com/mk6ZKsiIzT

— Scarborough Subway Extension (@ScarbSubwayEXT) December 13, 2023

The SSE project is being carved out with a behemoth of a tunnel boring machine (TBM), which was shipped in parts from Germany before arriving at a launch site at Sheppard Avenue and McCowan Road in 2022.

This almost seven-kilometre-long dig commenced back in January, and has been pressing forward at full steam for close to a year now.

A titan of a machine is about to dig out the largest subway tunnel in Toronto history https://t.co/idsSgcQkpH #Toronto

— blogTO (@blogTO) January 21, 2022

The titanic earth-chewing machine was dubbed Diggy Scardust through a public naming competition. The playful moniker is a tribute to David Bowie's glam-rock alter ego, Ziggy Stardust, altered to reference the machine's 'dig' through 'Scar'borough.

Diggy Scardust moves at an almost imperceptible speed, chewing through an average of 10 to 15 metres of earth per day, and leaving behind tunnel liner sections, which are then anchored into place.

The excavated material is then transported back to the launch site, and fed along an extensive conveyor belt system for collection.

👀It's hard to convey the size of the conveyor belt system without showing it.

Seen from above at our Diggy Scardust (TBM) launch site @ Sheppard & McCowan, it measures in @ 2m wide with 8 separate conveyors moving materials up to 8m per second - what are we feeding this thing? pic.twitter.com/BWQnBPIS8b

— Scarborough Subway Extension (@ScarbSubwayEXT) November 30, 2023

A Metrolinx representative tells blogTO that Diggy "has progressed 832 metres from the launch shaft."

Metrolinx says that following its impressive first burst of progress, the machine is currently halted, as it "is currently undergoing planned maintenance ahead of significant progress expected in 2024."

The public will be able to keep close tabs on the TBM's progress starting in the new year, when Metrolinx will launch an online TBM tracker, similar to the tracking pages made publicly available for the Eglinton Crosstown LRT's tunnelling phase, as well as the line's ongoing western extension.

Tunnelling for the project is expected to take between two and three years, though it will still be a while longer before the public can ride in this massive record-breaking tube.

Here's what Toronto's new TTC Scarborough subway extension stations will look like https://t.co/u2DlYAlUL9 #Toronto #TTC

— blogTO (@blogTO) December 22, 2022

The Scarborough Subway Extension is currently estimated for completion in 2030.