Hi Afif -- It sounds like you have an 8 reales silver cob coin from Bolivia. There are a few other possibilities based on the description you supplied, but this is the most likely.
Be aware that these coins are valuable and heavily counterfeited.
The 8 reales in our main picture (upper right) comes from Daniel Sedwick Coins in Winter Park, Florida USA. It is in good shape and you can read the 1654 date. This specimen sold at auction for $525 US dollars during 2013. This gives an idea of value of these interesting and desirable coins. CoinQuest thanks Mr. Sedwick for use of his coin photo. It's a nice coin.
The denomination '8' shows a the top center of the 'pillars and waves' side of the coin. The 'P' before the '8' indicates the Potosi, Bolivia mint. If your coin has an 'L' in place of the 'P', it was minted in Lima, Peru (see this page [Press Here]).
There is tremendous variation in these coins, and each coin stands on its own merits. The valuations below are very approximate. If your coin has a readable date and is not too far off center, those are good things and your coin will be more valuable than those without date and far off center. The catalog values below are for coins with readable dates. If you can't find the date, divide the values by two.
1 REAL (approx 18 mm diameter)
worn: $40 US dollars approximate catalog value
average circulated: $100
well preserved: $200
2 REALES (approx 23 mm diameter)
worn: $50 US dollars approximate catalog value
average circulated: $150
well preserved: $300
4 REALES (approx 30 mm diameter)
worn: $100 US dollars approximate catalog value
average circulated: $350
well preserved: $700
8 REALES (approx 40 mm diameter)
worn: $120 US dollars approximate catalog value
average circulated: $400
well preserved: $800
If you have a nice specimen, by all means find a knowledgeable collector or professional coin dealer to inspect your coin in person.