Doors Open is the most rare of Toronto events: widely anticipated, universally loved, well attended, and free. Every year, tens of thousands of locals and tourists (and more than a few Torontoist Flickr Poolers) lace up their walking shoes and descend on the participating sites, learning about architecture and history while exploring rarely seen parts of the city. And with 175 buildings on the slate this year, there's lots for everyone to enjoy. But it's impossible to look at the full list of venues and not wonder about the buildings that don't appear. Maybe they've never taken part or maybe they're simply taking this weekend off. Either way, here are a few of the sites we'll miss this year.
Some of Toronto's most iconic structures are conspicuous by their absence. Why does the CN Tower not participate in Doors Open? Or the neighbouring SkyDome? Where's our view into the Royal York or King Edward Hotels? The Sharp Centre at OCAD? ROM Crystal? AGO? Granted, not every building can participate every year, but it seems peculiar to celebrate Toronto's architecture without including some of Toronto's most celebrated architecture (or at least its most identifiable architecture).
Some of the best exhibits from previous years are no longer taking part. Perennial favourite Redpath Sugar Museum is missing its second year in a row. Although the Canada Life building is participating this year, its remarkable Environmental Room, a tropical ecosystem complete with breathing wall and aquatic habitat surrounding a meeting room, was torn out of the complex a few years ago. And then there are the Wychwood Streetcar Barns. Never to be viewed again as a decrepit repair facility, it was recently reborn as a living artistic community. We hope for similar fates for some other crumbling landmarks.
Torontonians have proven themselves to be infrastructure geeks, but the gorgeous R.C. Harris Water Treatment Plant remains shuttered to public tours in continuing overreaction to perceived terrorist threats. Inside views of the city's sign shop, the decommissioned Hearn Generating Station, the Ashbridges Bay Wastewater Treatment Plant (especially stinky at this time of year), and even the locally reviled Portlands Energy Centre would likely be popular, but the city's machinery, both current and former, remains largely ignored during Doors Open.
Have you ever wondered why there's an old tugboat docked in a large sunken box at Exhibition Place? The Ned Hanlan is docked beside the Stanley Barracks, home for years to the Toronto Marine Museum. What's that? Toronto has a marine museum? Not any more. Shortly after a high-profile and ultimately disastrous move to Harbourfront, the museum was closed and its exhibits put into storage as a cost-cutting measure. All three venues—the Stanley Barracks, the Marine Musuem, and the Ned Hanlan—are forgotten or all but invisible to the public. Let's bring at least one of them back.
Photo of HMCS Haida being towed out of its berth at Ontario Place by Val Dodge.
But there's hope for the future: the New Broadview House Hotel (currently dominated by strip club Jilly's on the ground floor) on Queen Street East has been touted as a possible site for an east-end analogue of the Gladstone and will make a welcome addition to the Doors Open lineup in five years. For even further down the road, maybe we can we look forward to the unearthed and reconstructed Teiaiagon or Ganatsekwyagon, or public tours of architectural digs around the Knapp Roller Boat, the still-buried eastern section of Queen's Wharf, or the first Parliament buildings.
Of course, none of this wishful thinking is going to stop us from enjoying Doors Open this weekend. We'll be strolling down the streets with everyone else, discussing not only the buildings we've just seen, but the ones we hope to see next year.

Elsewhere in the Ist-a-Verse
infiltration:
love it - mostly too shy.
I love your caption for the HMCS Haida photo, which makes it sound like Val Dodge is a tugboat captain, or perhaps the tugboat itself.
adorable
Hearn? Are you kidding? That place is an active demolition site. No way it would be opened, especially given the death there last year.
That doesn't mean that people don't want to see it. The Brick Works, the Don Jail, and the Wychwood Streetcar Barns were also hazardous sites that have been open during previous events. The Brick Works is open this year despite its current state of reconstruction, and the Don Jail has loading restrictions in place. So why not Hearn? I'm not saying that people should have free run of the place, but surely there's somewhere for people to stand and look inside.
Just the scale of demolition at R.L. Hearn has made the site far more dangerous than any of the places you've listed. Also, at this point, little remains of what made the site unique to begin with - the turbine deck was ripped out over two years ago and I can't see them letting anyone near the control room (given it's proximity to said torn up turbine deck).
Another once-upon-a-time Doors Open attraction worth noting: Toronto Island Airport...
And yet another, in light of architectural news of the past week: Roy Thomson Hall...