Complex sentence: The hill was private property for many years, formerly being part of a game estate (an old shooting box can still be seen on the flanks of the hill), but it is now managed by the National Trust and is open to the public.
Split into simpler sentences: The hill was private property for many years, formerly being part of a game estate; an old shooting box can still be seen on the flanks of the hill. It is now managed by the National Trust and is open to the public.