I've been riding 28km to work once or twice a week on my cheapo single-speed fatty (Canadian Tire version of the Mongoose Beast, the Schwinn Biggity). There are a couple of minor hills but nothing big or I'd have to walk up. It's slow & it's heavy but it's fun to ride & was cheap & has convinced me to eventually spend more on a better, geared fatty with brakes.

Not sure I'd recommend it for a commute though I do enjoy commuting on it.

Cheers