Shuffling along the city streets in Vancouver we don't often pay attention to what's underfoot.
And why would we? It's usually concrete or a steam grate. But every now and then, patches of purple glass tiles, cracked, worn, and half buried in concrete will appear and give a glimpse into the world of subterranean tunnels that Vancouver used to have.
The tiles, called sidewalk prisms, are largely contained to the downtown core and are remnants of "areaway" roof structures.
What's an "areaway"? According to an emailed statement from the City of Vancouver, "areaways are underground structures that are typically an extension of a commercial building’s basement under the sidewalk. This means the roof structure of an areaway supports or acts as the sidewalk surface above."
Areaways date back to the early 1900s and the glass tiles were incorporated into the sidewalk to let light filter into the underground spaces. The city says that the prevailing theory around as to why the glass is purple was a result of a UV light reaction that changed the composition of the glass over time.
Are Vancouver's areaways still open?
Sidewalk prisms are found in cities all over the west coast of North America from Vancouver to San Francisco with the most famous example being Seattle which runs tours through the vast network of tunnels.
In other cities, like Vancouver, most areaways have been decommissioned over the years as street and utility upgrades and redevelopment takes place. "In modern cities, the area below sidewalks is used primarily for important telecommunications and utilities corridors," the city reports.
The areaway structures are owned and maintained by the individual property owners but some remaining glass blocks have been paved over when damaged to ensure sidewalks remain safe and accessible.
Even though some buildings maintain areaways to this day, there are fewer than 25 locations in Vancouver where the glass blocks still exist.
"Design and performance requirements for new sidewalks have changed significantly in the last 100 years," the city tells V.I.A
"All new walking surfaces need to be suitable for wet and dry conditions and must be able to support the weight of emergency vehicles. As many of the glass manufacturers are no longer in business due to the decrease in demand, and since concrete and steel are more efficient at meeting these requirements, glass prism blocks are rarely used today."