I don’t think there is AgentOrange. The country is pocketed with heathland, commoners grazing pastures, woodland trails, riverside trails and locally permissive paths. All unmarked on the map but visible, signed and accessible when you get there.
To look at one of my favourite short local walks on a map would have you thinking I’m recreating the Kinder Mass Trespass, but I’m not. Not that I’d care if I was mindst, but that’s a different story.
It may be just me but I quite enjoy “happening upon” these little pockets of unrecognised adventure on my walks. I even do a walk to see what’s at the end of a seemingly “dead end” PRoW. Most times it leads to nothing but sometimes it leads to a hidden patch of heathland. Near me there’s a substantial lake that isn’t on the map despite a PRoW going right past it and signs round it saying no right of way (but there’s still a trail round it if you care to walk round the back a ways which leads to a lovely private memorial). I’m guessing a relative of the owner of the land.
Something else I think; memories from my childhood. We didn’t care (or know) about access land or PRoWs. We just played out, in the woodland, in the farmers fields, played ball games on random patches of scrubby grass in the middle of nowhere. Revisiting these childhood places recently had me realising that just because there isn’t a path on a map doesn’t mean we can’t walk there.
Granted, it doesn’t help with planning a walk when poring over a map of an unfamiliar place but to do a walk “just to see what’s there” certainly keeps the sense of adventure alive