In the Toronto subway there is the University segment of line 1. The part from Osgoode Station to Museum Station was tunnelled, and as they do remediation work in the station, you can see how it was built… early 1960s style. Both Queen’s Park and St. Patrick stations have unique tube-like appearances that are reminiscence of the London Underground. What is interesting is that they pre-date the use of concrete tunnel linings, and instead use curved sections of cast iron tunnel lining, held together with bolts.
For tunnels that are nearly 60 years old, the sections of cast iron almost look as if they were installed a couple of years ago. Concrete likely trumps cast iron from the viewpoint of speed, versatility, and strength, but there is something intrinsically appealing about the nuts and bolts of cast iron – almost Meccano-like.