Infinity Candle

The Infinity Candle was created by the British designer Nick Moore. They come in different shapes and sizes, but the basic principle is constant. At the back is a mirror, and at the front is a half silvered mirror. In between the two mirrors you place a lighted candle. The action of the two mirrors produces an optical illusion of infinite regress - it appears that there is a whole row of candles stretching away into the distance.

You can get a similar effect in a lift which has mirrors on both sides - when you hold your arm out, you seem to see an infinite array of arms.

These are fairly widely available in retail stores.