Obsidian Farm

turtle.forward()
turtle.forward()
while ( turtle.getItemCount(16) > 0 ) do
    for i = 1, 6, 1 do
        turtle.digDown()
        turtle.select(16)
        turtle.placeDown()
        turtle.forward()
    end
    turtle.turnRight()
    turtle.turnRight()
end
turtle.forward()
turtle.forward()
turtle.turnRight()
turtle.turnRight()