Easy As Pie

Here's the original definition of "cakewalk":

A 19th-century public entertainment among African Americans in which walkers performing the most accomplished or amusing steps won cakes as prizes.

It may have been fun, but was it that effortless? Sounds like it could be pretty tiring. (Though not as bad as a Turkey Trot.)

On the other hand, it does explain the phrase "take the cake."