It is illegal to photograph official buildings. Verify with local authorities before taking photos.
Smoking in public places in Costa Rica is prohibited. You’ll see the signs everywhere. If you’re caught by the police, you will get a fine (minimum of 180,000 CRC which is about 320 USD!).
Don’t bathe nude – you won’t get fined for it, but it’s not acceptable in Costa Rica.
Don’t pick plants or hunt for seashells. And don't damage trees or flowers, no matter how beautiful and irresistible they are! In Costa Rica, vegetation is strictly protected by the government and it could be the equivalent of a felony if you are caught disturbing the flora and fauna.
Drug dealing is illegal. Drugs are cheap and plentiful in Costa Rica, especially cocaine. However, the drug laws are very strict and you would be very lucky to find a lenient police officer if you’re caught buying or possessing drugs. The last way you want to spend your Costa Rican vacation is locked up in a scorching hot prison.