What this coin looks like (obverse, reverse, mint mark location, special features, etc.):
The 1866 Five Cent Shield Nickel had a RPD error in which the 1866 date was repunched over another 1866 date. Typically this can be seen by noticing the numbers of the underlying date appearing between the numbers of the primary date as depicted by the arrows in the example image above.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD