The Right of Public Access
The right of public access, which seems to be quite unique for Sweden, Finland, Norway and Iceland, is an ancient common law that gives anybody the freedom to roam basically wherever they want in woods and fields.
To us Swedes this right is so self-evident that we perhaps don't realise how lucky we are in this respect (as in many others, for sure). Our access to our natural surroundings is more or less unlimited. We can pick wild berries, flowers and mushrooms without asking the landowner's permission, and out of sight from the nearest house it's possible to put up a tent for one night before permission is required.
Of course, with privilege comes responsibility, and there are a few things to keep in mind in order not to violate the right of public access. Naturally, you won't become very popular if you walk into other people's gardens and pick their strawberries, and you definitely should not chop down trees for firewood when you're out camping! Nor will the farmer be amused if you clomp around in a field where crops are being grown, but in the end all this is really no more than common sense.