Windsor Castle is not a ruin and not a film set. It is a working royal residence, which means rooms close when the household needs them and the State Apartments are the visit, not the whole town. The castle sits on a hill above a Thames-side high street that exists largely to feed you afterwards.
The Long Walk, running south into the Great Park, is free and the right way to see the walls before you decide whether the ticket is your morning.
See
The castle, booked
Timed entry. St George’s Chapel is the architectural point, when it is open to visitors. Check the day’s closures before you travel.
The Long Walk
Three miles of grass if you go to the end. Even twenty minutes reframes the walls.
Eton, across the bridge
A different town, a school, and a high street. Fifteen minutes on foot. Do not try to tour the school as if it were a second castle.
The river path
Downstream or up, away from the coach drop. Swans are not a personality.