Why Costa Rica? Be careful down there. I've never been there, but frankly some of them S./Central American Countries seem a bit scary. I saw a story about 2 girls who went to CR, they wound up in bad company, were raped and murdered. Sure, that can happen anywhere, but in some of those countries "life is cheap." (I just saw the movie 'Blow', and that's what the Columbian character told Depp's character)
Hopefully you'll be in a good area.
Watch out for pick-pockets and street kid gangs.