Niue, a sovereign state in free association with New Zealand, uses two official legal tender currencies. The New Zealand Dollar is the circulation currency for daily transactions, while the government also authorises legal tender coins in the Niue Dollar currency for collector's purposes.
A number of mints issue a large variety of commemorative, bullion and collector coins under the authority of Niue. These coins are dedicated to historical or general popular culture themes not related to Niue itself. Many of them are in standard bullion sizes - typically, one ounce of silver (abbreviated as 1 oz Ag, where "Ag" comes from the Latin word for silver, Argentum). Many of these feature famous movie characters.
This coin is part of a New Zealand Mint series dedicated to DC Comic characters, and features Superman.
The Mint says about it:
This spectacular 1oz rectangular silver coin features iconic artwork from the DC Comic Superman #204. It shows a stunning coloured image of Superman in front of an engraved Metropolis skyline including the Daily Planet building. The obverse features the Ian Rank-Broadley effigy of Her Majesty Queen Elizabeth II, confirming it as a legal tender coin.
Inside the Superman-themed box a magnetised acrylic coin case allows easy display and access to this incredibly detailed coin. | 
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