The Leslie Street Spit is a human-built headland that stretches 5km long into Lake Ontario. The beach is a "landfill park" made of garbage, mostly construction waste, which is slowly degrading.
The spit was originally constructed in the 1950s as part of a plan to increase capacity of the Toronto Harbour, but shipping volumes in Toronto did not rise as expected, and the city ended up not needing an extra harbour after all.
Since then the spit has been colonized by plant life, and is now formally recognized as an Important Bird Area. On the beaches, you can find brand-new bricks, chunks of concrete and their rebar, pieces of countertops, walls, pipes, and other leftover parts of the city.