There's a lovely trail in Woolwich township, about a five minute drive from the Waterloo market (and from my workplace). It's at the first bridge on Three Bridges Road.
The bridge is an old Mennonite horse bridge. It isn't fancy but it's a nifty design: low and flat, when the river is in flood the water flows over the top. Horses can cross through the water, and there are poles that make the boundaries of the bridge visible to them.
In the 19th century there was a Mennonite mill near the bridge, but all that's left is the waterfall and mill race. The trail follows the old mill race all the way to St. Jacobs and beyond. It's a charming walk.
Here are some shots from the trail.
Three Bridges Road starts at Lobsinger Line (the road that runs between Heidelberg and King Street). Just a couple of minutes drive down Three Bridges, the road takes a 90 degree turn and you're there... there are pull-overs for parking right before the bridge. Here's a map. The red dot marks the spot: