Public footpaths. Public bridleway. Public byways. A piece of land (in England or Wales) that the public have a legally protected right to access at anytime. The UK government has an entire website section dedicated to the subject. Many of these paths are hundreds of years old and cover thousands of miles.
I love to explore these public right of ways whenever I get the chance. On my way home from Sussex last week, I briefly explored one. It had just rained. The forest smelled clean and fresh. The only noise I heard was from a passing sparrow. Magical.