The Garrison Creek used to run through Trinity Bellwoods Park and a remnant of its waterflow ravine is the bowl or hollow in the middle of the park. The creek is now buried as a sewer pipe.
GARRISON CREEK HISTORY
The Lost Rivers Walks Project is a joint effort by Toronto Field Naturalists and Toronto Green Community. They've produced a wonderfully informative page about the Garrison Creek's history from pre-contact times to recent neighborhood efforts to acknowledge and rediscover this natural waterway. You can find more about all the Toronto lost river walks they've documented at their index page.
Photo thanks to Toronto Green Community
SELF-GUIDED GARRISON CREEK WALK
A number of park neighbors were involved in creating a Discovery Walk which illuminates the creek's history. Check out the pdf of a self-guided walk which traces the creek from Christie Pits park down through Fred Hamilton, Trinity Bellwoods, and Stanley parks to Fort York. Skipping from park to park as the land slopes toward the lake is like finding a trail of secret gardens -- especially magic in the heat of the summer.