turtle (1.3 pr2; requires "sandbox")

-- starts just above -X -Y -Z facing +X
-- ends just above +X +Y +Z facing +X

local facingy = false

local function travel(dx, dy, dz)
    for k = 1, dz do turtle.up() end
    if dy ~= 0 then
        if not facingy then turtle.turnLeft() facingy=true end
        for k = 1, dy do turtle.forward() end
        for k = 1, -dy do turtle.back() end
    end
    if dx ~= 0 then
        if facingy then turtle.turnRight() facingy=false end
        for k = 1, dx do turtle.forward() end
        for k = 1, -dx do turtle.back() end
    end
    for k = 1, -dz do turtle.down() end
end

local function goto(x, y, z)
    local tx, ty, tz = turtle.gps()
    travel(x - tx, y - ty, z - tz)
end

local function make(size)
    if size == 1 then
        while not turtle.placeDown() do
            print("Out of blocks - refill and press enter!")
            read()
        end
        return
    end
    size=size/3
    local x, y, z = turtle.gps()
    local d = size - 1
    goto(x, y, z) make(size)
    goto(x+size, y, z) make(size)
    goto(x+size*2, y, z) make(size)
    goto(x+size*2, y+size, z) make(size)
    goto(x+size*2, y+size*2, z) make(size)
    goto(x+size, y+size*2, z) make(size)
    goto(x, y+size*2, z) make(size)
    goto(x, y+size, z) make(size)
    z = z + size
    goto(x, y, z) make(size)
    goto(x+size*2, y, z) make(size)
    goto(x+size*2, y+size*2, z) make(size)
    goto(x, y+size*2, z) make(size)
    z = z + size
    goto(x, y+size*2, z) make(size)
    goto(x, y+size, z) make(size)
    goto(x, y, z) make(size)
    goto(x+size, y, z) make(size)
    goto(x+size*2, y, z) make(size)
    goto(x+size*2, y+size, z) make(size)
    goto(x+size*2, y+size*2, z) make(size)
    goto(x+size, y+size*2, z) make(size)
end

make(81)