Simple Tunnel

local tunnelDepth = 24
local tunnels = 3

for tunnel = 1, tunnels do
  for i = 1, tunnelDepth do
    if turtle.detect() then
      turtle.dig()
    end
    turtle.forward()

    if turtle.detectDown() then
      turtle.digDown()
    end

    if turtle.detectUp() then
      turtle.digUp()
    end
  end

  for j = 1, tunnelDepth do
    turtle.back()
  end
  turtle.turnLeft()
  turtle.forward()
  turtle.turnRight()
end