This is the Best Answer for What goes into the blank????.... If you want to indicate yourself that that you went...SPANISH HELP!!?
riberas = shores (of a river)
costas = shores (of the sea or ocean)
playas = beaches
I went to Costa Rica ten months ago...
Yo fui a costa rica diez meses atrás.
PD. orillas is also correct for shores (river, sea or ocean's).