Hi Pino -- It sounds like you have an 8 reales silver cob coin from Peru. 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. See our page on counterfeit cob coin similar to this.
The coin in our main picture (upper left) is a 1 real coin minted in Lima, Peru. The denomination '1' shows a the top center of the 'pillars and waves' side of the coin. The 'L' before the '1' indicates the Lima mint. If your coin has a 'P' in place of the 'L', it was minted in Potosi, Bolivia (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: $30 US dollars approximate catalog value
average circulated: $80
well preserved: $150
2 REALES (approx 23 mm diameter)
worn: $60 US dollars approximate catalog value
average circulated: $150
well preserved: $250
4 REALES (approx 30 mm diameter)
worn: $100 US dollars approximate catalog value
average circulated: $250
well preserved: $500
8 REALES (approx 40 mm diameter)
worn: $120 US dollars approximate catalog value
average circulated: $350
well preserved: $600
If you have a nice specimen, by all means find a knowledgeable collector or professional coin dealer to inspect your coin in person.