Some of you can rightly scoff at this, judging by the wonderful regions I've seen on this thread, but hey, I have found myself a small slice of heaven amidst the (sub)urban jungle I live in: a Provincial Park within city limits, beside a creek that is protected from development. The ring road, for automobile access, measures out to a 4.8 kms. loop, with a whopping 20m of elevation change.
If I get there before the 8:00am opening time, I have this circuit all to myself. Zero worries about cars, few worries about dog walkers; my only real concern is dodging the snails caught napping on the warm pavement when they are "in season"!
This is literally beside one of the busiest 6-lane highways in our region of southern Ontario, the Queen Elizabeth Way. In fact, I can hear the thunder of the traffic (commuters already clogging the highway at 6:30am) and yet never have to worry about what's coming over my shoulder. Just hammer hammer hammer, then ride ~ 5 kms to return home. To see the small scale of this route in a positive light, I figure the frequent hairpin turns help me practice my braking & shifting on my aero bars (P2 SL) so that my bike handling skills will be far above those of an average triathlete!
You can appreciate the proximity to the highway from this overhead view.
The starting point/turnaround hairpin. The childrens' "play barn" is to the left in the middle-distance. Office towers are to the right!

The lane widths are similar to an average street, each direction running separately. The return lane can be seen to the left.
Several intersections occur to access various parking lots. But at 6:30am... no cross traffic!
Running parallel to the roadway, I flatter myself by pacing the vehicles (momentarily... as they accelerate away from the gas station driveways)
The road surface, I've got to say, is uniformly excellent. Snails notwithstanding.
Just past the curve ahead is the far turnaround hairpin. The highway's exit ramp light standards can be seen over the embankment. So close, so far...
The "out" lane is in the foreground, seen from the return lane. Yes, being Canada, you're never far from the ubiquitous Tim Horton's!
On one side: a franchise donut shop; on the other: chickens, sheep, cows, peacocks. And me in the middle, on the aero bars, a big stupid smile on my face.
The original start/turnaround again, viewed from behind. Still trying to make each circuit under 8 mins, but hey - it's about the journey! I do as many laps as time and my constitution permit.