We went for a lovely walk with my family yesterday in the grounds of Blenheim Palace. There are a few public rights of way through the grounds, which you do not need to pay to use. The one we prefer begins on the A44 (“The Causeway”) here
You enter through the green gate marked “95”
All this is shown on Google maps and the Ordnance Survey (grid ref SP435165) shows the rights of way.
Cheers for this, I cycled up to blenheim from oxford the other day and was disappointed because I wanted to explore the grounds but was put off by the £9.50 entrance fee. Funny the staff don’t tell you about these entrances…