Brockville Tunnel

For a hundred years, trains traveled through this tunnel to access the shipping docks on the St. Lawrence River. Then in the 1960s the passage was abandoned, and it remained empty for about half a century. Now, it is enjoying use once again, this time as the highlight of a walking trail that leads to the waterfront in Brockville, Ontario.

Opened in 1860, this railway tunnel is the oldest in Canada. It's also one of only a few railway tunnels in the world with doors at each end. According to local lore, this was to keep out the cattle that used to roam the streets, but more likely it was meant to provide some winter protection and deter the townspeople from entering the tunnel.

In any case, the doors now open to a popular walkway about a third of a mile long, illuminated in a rainbow of hues by thousands of colorful LED lights, and filled with the sounds of music. On hot days the tunnel becomes a cool retreat, as the temperature remains a near-constant 55 degrees Fahrenheit year-round.

Technically inclined visitors may spot three different construction methods in this single tunnel, and because the tunnel was designed to allow water to penetrate (in order to reduce hydrostatic pressure against its walls), you may also notice mineral deposits forming at a much faster rate than those in natural caves.