Site just visited (November 2017). Initially I tried to visit some more places but all in all I managed to see only Finca 6. Currently due to high level of rainfall the site is oficially closed for visiting but after some negotiations with site guards I was able to see the site (althouh the exhibition part / museum was closed).

Finca 6 is easily accessible by bus from Palmar Norte town (take a bus heading to Sierpe and take off near the museum, its some 9 km from Palmar), come back the same way via Palmar Sur. The bus circulates every 45 minutes during the day. Entrance to the archeological site is around 300 m from the bus stop.

As everything was perfectly described by Esteban (great job done) I will focus on trying to find other sites. So after visiting Finca 6 I intend to see the closest place - Grijalba 2. I take off the bus near the airport and staretd to explore the area. After some hours of exploring places north of airport, questioning several local people I found nothing. Believe me - I spend some hours and local people can confirm that - it is not the place. Later on I realised that the coordinates of this particular place were completely wrong. The real place is located on the opposite side of the river, close to Osa municipalidad.

Correct location of Grijalba 2 archeological site are as follows: 8.981078, -83.522018, you can check that on official municipality page - http://www.gobiernolocalosa.go.cr/turismo/info.php?item=59

Other place seem to be correctly identified - El Silencio - the biggest sphere found in the area and Batambal. Mind that there are no signs of the places so you should rely on GPS coordinates when trying to find them.