This might not yield much in the sense of exploring, but might be interesting for general infrastructure porn.

There currently is a pretty big water main construction happening, mostly underground in Downtown Toronto, documentation is here:
http://www1.toront...10000071d60f89RCRD

I stumbled upon this by chance one day and could not resist taking a picture down the hole. From outside the construction side the hole looks not very interesting, only looking over the railing yields the real look down. The picture was taken at the end of last year, McCaul/D'Arcy intersection.

click to view

Pretty bad ass, you can see the tiny railway running at the bottom. The open access shafts are documented on the page.
The work is nearly done meanwhile as far as I can tell, I cycled by one site today and the hole is visibly filled half way, with only a smaller access shaft remaining. This is visible even from outside of the construction site.

Also, they will rip open the Spadina/Dundas intersection from July 14 to July 28, which is pretty close so might be related and a pretty deep hole. Maybe not.

Really cool stuff. Hopefully someone will have a chance to check it out.