On Monday afternoon a hydro vault exploded beneath Bay and King, sparking an electrical fire with an unpleasant odour.

While Toronto Hydro says precise answers about the cause of the fire will take time, spokesperson Tori Gass told Metro they will “look at any and all possible contributing factors which could include infrastructure and weather.”

Beyond the Lost-like cloud of black smoke, we take a look at some of the other mysteries that lurk beneath the surface of Toronto.

Read more:

Smoke outside RBC building in downtown Toronto caused by a hydro fire

King St. W. still closed after hydro vault explosion

Transformers: They’re more than meets the eye. It may have been a transformer at the centre of Monday’s incident, but they’re a necessary part of delivering power to your home. According to Kate Ascher’s book The Works, large transformers at the power plant increase the voltage so electricity can travel long distances. Then the voltage is reduced at another transformer to a level appropriate for homes and businesses.

Buried rivers and creeks: Toronto used to have more rivers and creeks until their smell and perceived threat to public health led to their unceremonious burial. But you can still find signs of Garrison, Taddle and Ashbridge’s Creek throughout the city.

Taddle Creek is the reason for Queen’s Park Crescent’s crooked southwest curve, and the buried Garrison is why there’s a concrete bridge in Trinity Bellwoods Park that now serves no purpose.

Police cordoned off a busy downtown Toronto intersection on May 1 as blasts were heard and thick smoke billowed from a grate. Toronto?s fire chief says the issue was due to a hydro vault fire, which is under control.

Energy balloons: Dive 60 metres below the surface of Lake Ontario and you’ll see giant balloons that store surplus energy for island residents. It’s part of a two-year pilot project by Toronto Hydro and local energy firm Hydrostor and can power 330 homes.

Pneumatic Tubes: Before email and Slack, some Toronto journalists filed their stories using a series of underground pneumatic tubes. While the tubes are mostly if not entirely gone as a result of various construction projects, they used to link Old City Hall to the offices of the Toronto Star and Toronto Telegram.

Lower Bay and Lower Queen stations: These secret stations are only occasionally opened to the public.

Lower Queen was originally intended as an east-west streetcar-subway line, but it never got built.

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Lower Bay was built for a 1960s transit experiment in which subway cars would use both the Yonge-University and Bloor-Danforth lines on one trip.

Now Lower Bay is used for film shoots like Johnny Mnemonic, Max Payne and the Academy Award-winning Suicide Squad.