Now in its 16th year, the annual Doors Open festival has given millions of Torontonians the chance to discover parts of the city that are often closed to the public. In total, more than 450 Toronto buildings have participated over the last decade and a half, making it one of the most popular events of its kind in the world.

Still, despite all the excellent places to snoop around this year, there are numerous buildings in Toronto that still remain firmly closed to the public. Often there are safety or security concerns, but in several cases the necessary accommodations could be made with a little creative thinking.

Here are 5 buildings we wish were part of Doors Open, but probably never will be.

The Whitney Block
Opened in the 1930s, the central tower of the Whitney Block (pictured above) on the east side of Queens Park Crescent is an overlooked Toronto architectural wonder.

Disused since 1968 due to a troubling lack of fire escapes, the sixteen-storey tower resembles Commerce Court North on King St. and is ornately decorated with sculptures depicting justice, tolerance, wisdom and power. Others show mining, farming, forestry, finance, law, and education. The public isn't allowed inside. Not even for a peek.

Commerce Court North
The banking hall is impressive, no doubt, but the part of the building everyone really wants to see is the rooftop observation deck.

Though it has ostensibly been closed for safety reasons since the 1960s, CIBC does occasionally grant access to visitors. The panoramic view has been obscured somewhat by architect I. M. Pei's Commerce Court West tower, but those giant sculpted heads are what everyone really wants to see up close.

TTC Transit Control
The Toronto Transit Commission manages the entire subway--trains, signals, switches, and more--from a secure control room kept hidden from the prying eyes of the public. We occasionally catch glimpses of it via B-roll during the TTC's explainer videos, but otherwise the high-tech control room is shrouded in mystery.

The Scotia Plaza bullion vault
The deepest basement in downtown Toronto is home to a dazzling bounty. Shelves of solid gold bars line the Scotiabank bullion vault under the bank's red Napoleon granite Toronto headquarters.

As you might expect, the bank doesn't allow visitors and generally won't discus what's down there, or how much it's all worth. An urban vault belonging to Scotiabank was destroyed during 9/11. The value of the gold and silver bars recovered from the wreckages was about $200 million.

AGO art vault
There are more than 73,000 works in the Art Gallery of Ontario's collection, and most of it is stored in a high-security facility on Dundas St. The AGO used to let its members in for a nose around, but there are no plans to do so in the future.

Chris Bateman is a staff writer at blogTO. Follow him on Twitter at @chrisbateman.

Image: Michael Harvie, Marcanadian, James Anok, Peter Crock/blogTO Flickr pool.