I just stumbled upon this photo of what appears to be a reasonably normal citybike, except it looks like it has a second set of pedals at the rear wheel.
Anybody knows what it is?
There are bicycles with a crankshaft that runs through the rear axle. The "Tur Meccanica Bi Bici" is such a bicycle:
I can't tell from your picture if it's the same bike or not, but it certainly could be.