I'm trying to make a ramp/sidewalk that starts at door threshold level and ends at street level which is roughly 3' lower in elevation. I would like to make the sidewalk in a horse shoe shape. How can I make this a continuous, descending slope that curves in the middle?

I'm trying to make a ramp/sidewalk that starts at door threshold level and ends at street level which is roughly 3' lower in elevation. I would like to make the sidewalk in a horse shoe shape. How can I make this a continuous, descending slope that curves in the middle?