I spent part of my childhood living in the little coal-mining town of Kemmerer, Wyoming. One of Kemmerer's claims to fame was the fact that instead of having a Town Square, Kemmerer's business district featured a triangle at the center. As a kid, I thought that was pretty neat.
Kemmerer's triangle park isn't quite one-of-a-kind, though ... there's a triangular park in the middle of downtown Wolf Point, too. It's called Sherman Park, and it's not quite the perfect equilateral that an urban planner might draw -- instead, it's an artifact caused by two sets of platted street grids that don't align quite right. But still, it gives the place a bit of cachet.
Here's a very early aerial photograph of Wolf Point's uniquely-arranged business district. The large building facing the park was the Sherman Hotel, the largest hostelry for miles around. Unfortunately the hotel was destroyed a while back -- in a fire, I think -- and today the Sherman is just a boxy, ordinary motel.