Translation:Walking down is easy.
This Chinese sentence can be used as an encouragement to someone who is about to go down a steep ladder or staircases, or as a description of the way to a lower place, e.g. a destination downhill. In such context we can say "It is (pretty) easy to go down there."
"下去" actually can also mean "to continue to" do something. Then in such context it would not necessary mean there is a different in altitude. "走" is also often used in a metaphorical way to say to lead the way of life. It is better to ignore these meanings first, given the constant lack of context in Duo.
Agreed. While you're most likely to hear this sentence in a metaphorical sense, as in "the path ahead/what to do next within a given situation or project/continuing or completing a plan or method" being easy, on Duolingo it's generally good practice to use the most literal translation.
I think there's an implied "there" here as there was in previous direction complement exercises and therefore "Walking down there is easy." should be permitted.
So does this mean downhill? Otherwise I can only think of walking down stairs or some kind of slope...
in the "type what you hear" exercise the anwser gets marked wrong until you add the " . " at the end of the sentence