@Chickwit I second the suggestions by
@HelenP As far as an easy challenge, I'm not sure the Rival Dynasties Challenge (RDC) would be the answer, considering that no one has yet to complete the challenge since its unveiling a year ago.
The tournament challenges are the perfect way to hone your gameplay skills and pick up awesome tips about a wide variety of gameplay aspects.
A tournament can run as short as the young adult phase (20 sim-days) or a combo of both the young adult and adult phases (40 sim-days).
The Wonder Child Challenge lasts roughly 32+ days from the Wonder Child's conception by an adult couple. It's a fun challenge, regardless of whether you keep score or not.
I've read the rules and stories based on the Drifter Challenge, recommended by
@Whirligig; I'm not sure it would qualify as an easy challenge.
That's just me, though, since I'm not into building very much.