A bicycle with a full chain case. They're hard to find in the U.S. Bike mechanics say it's because they're a pain to work on, but the cool thing is that you hardly ever have to work on them. When riding in the winter, I'd have to clean the gears and chain every couple of weeks, and then replace the drivetrain almost every year. With the chain case, so far my maintenance has consisted of oiling the chain a handful of times in three years.