Inspired by Philippo demo I wrote this ) You can control with the cursor.

-- 'tunnel' mini-demo by Al Rado
-- constants, change them for different effects
SCR_WIDTH = 240
SCR_HEIGHT = 136
MAX_COLOR = 15
COLOR_SWITCH_PERIOD = 100
COLOR_MOVE_SPEED = 2
SPEED = 1/800
DEVIATION = 150
RECT_STEP = 4
RECT_START_W = 30
RECT_START_H = 15
SIN_COEFF = 0.67 
SHIFT_DELTA = 0.03
-- variables
shiftX = 0
shiftY = 0
function TIC()
  if btn(0) then shiftY=shiftY-SHIFT_DELTA end
  if btn(1) then shiftY=shiftY+SHIFT_DELTA end
  if btn(2) then shiftX=shiftX-SHIFT_DELTA end
  if btn(3) then shiftX=shiftX+SHIFT_DELTA end
  -- calc base variables 
  slowedTime = time()*SPEED
  rectCount = (SCR_WIDTH - RECT_START_W)/ RECT_STEP
  -- draw rectangles
  cls()
  for i=0, rectCount do  
    stepX = (SCR_WIDTH - RECT_START_W)/ rectCount
    stepY = (SCR_HEIGHT - RECT_START_H)/ rectCount
    width = RECT_START_W + i*stepX
    height = RECT_START_H + i*stepY
    x = (math.cos(slowedTime) + shiftX) * DEVIATION/i
    y = (math.sin(slowedTime*SIN_COEFF) + shiftY) * DEVIATION/i
    color = (i/COLOR_SWITCH_PERIOD - slowedTime*COLOR_MOVE_SPEED)%MAX_COLOR + 1
    rectb(SCR_WIDTH/2 + x - width/2, SCR_HEIGHT/2 + y - height/2, 
      width, height, color)
  end 
  -- additionall draw 
  rectb(0, 0, SCR_WIDTH, SCR_HEIGHT, color)
  poke(0x3FF8, color)
end