I had a message from a young tico friend (mid 20's) who mentioned going to a big party. He said it was one of three held each year. I asked for more info and he wrote this.
CR main party events are:
1. Palmares (usually being held last week of January and first week of
February): 2nd place in the world for beer consumption per capita, after
Oktoberfest.
2. End-year break @ Guanacaste: daily parties, different each year... except year-end Espinar party, being held Dec 28th @ Filadelfia (Guanacaste); great party, maybe 2000-4000 people.
3. Half-year break @ Liberia: it's only a weekend, the Friday close to July
28th and the Saturday close to July 28th, there's another Espinar party on
Saturday, it was last Saturday, I had a great time
If you plan to attend any of the parties, I recommend Palmares.
You should definitely go with someone, Palmares is 1:30h away from San
José... going in car is fun but you can't drink (lot of policemen).
I recommend bus (such a cultural experience because you see a lot of
people's behaviour, but it's difficult to get a space and lot of people in
each bus) or cab (kinda expensive).
No party for you 
