Yesterday I made reference to a "secret picnic." S. invited a few friends to help perpetuate her tradition of a "trespasser's picnic," where you have your lunch in an idyllic spot that's somehow...off-limits.
Of course your purpose is benign. You have no wish to intrude. You simply know of a spot. No one's using it, it's perfect, and shouldn't someone have a picnic there?
When you leave, you take with you every bit of what you brought. "Pack out what you pack in," as they say, and no one will ever know you were there.