There's a secret world hidden behind the windows of Chicago in Watch Dogs. In future Chicago, one computer program controls everything in the city, from the power grid to rocking horse rides. There are other strange things about the city as well, like how every window reflects some mysterious bizarro city made almost entirely of straight roads.
You're standing on a hotel balcony with a big neon sign outside. You look in the window, and BAM! you're looking into an intersection.
You're standing in front of an office building by a statue, and you look in the window — BOOM — intersection. Driving your car parallel to some shop windows, INTERSECTION There's even an alternate world inside some buildings (via reddit): What's this alternate reality chicago like? There aren't any people there, so maybe it's more peaceful. Or maybe that's what it looks like after ctOS kills all the humans.
There is one hint — one of the studios that worked on the game? Ubisoft Reflections.