if you're just worried about actually getting caught, any isolated place will do. if you care about following the law strictly, it can be nontrivial to figure out what's allowed. there are federal, state, and local rules about where drones can be flown, and they are sometimes written in weird ways.
as an example:
> Launching, landing, or operating an unmanned aircraft from or on lands and waters administered by the National Park Service within the boundaries of [insert name of park] is prohibited except as approved in writing by the superintendent.
depending on how you interpret "operating", it might be legal to launch your drone just outside the park limits, stand there with the controller, and then fly it all over the park to your heart's content (provided you land it back outside the park). if an official actually saw you doing this, they might hassle you without regard for the nuance of the law.