2

local height = 0

turtle.dig()
turtle.forward()
turtle.dig()

while turtle.digUp() do
  turtle.up()
  turtle.dig()
  height = height + 1
end

turtle.turnRight()
turtle.dig()
turtle.forward()
turtle.turnLeft()
turtle.dig()

while height > 0 do
  height = height - 1
  turtle.digDown()
  turtle.down()
  turtle.dig()
end