Munette -- What you have is a single coin from a commemorative set of 4 coins. The set comes in a booklet distributed in 1988, marking the 500th anniversary of Portugal's Bartolomeu Dias's epic voyage around the Cape of Good Hope in South Africa, which made him the first man to have navigated the sea route between Europe and the Indian Ocean.
The four coins were made in South Africa and the composition is steel and bronze. The coins comes with a small brochures with history presented in three languages: Portuguese, English and Afrikaans. Descriptions of the coins:
AGOSTO 1487 - DEZEMBRO 1488 * LISBOA
SAO GREGORIO * MARC,O 1488
FEVEREIRO 1488 * AGUADA DE SAO BRAS
JANEIRO 1488 * RIO DOS VAQUEIROS
Each coin, if fully uncirculated and sold separately, brings one or two US dollars. A complete set is worth more, up to $20. But, to bring $20, both the coins and the packaging must be in tip-top shape. Worn packaging lowers the value dramatically.