Windsor Castle

You cannot use your Oyster card to get to Windsor via the train.
Your best bet is to get a same day return from Paddington - Windsor (with an easy change at Slough. The cost is about £10.80?.

The question of a line waiting to get in is a tough call.

I emailed the visitor info staff at Buckingham Palace a couple of weeks ago because I'd read somewhere that you could purchase tickets to Windsor Castle at a discount at BP. The answer is yes but only while you are on the State Rooms tour at Buckingham Palace. Given that BP doesn't open for tours until 22 July, this isn't an option for you.

I'm visiting Windsor next week and bought my print-at-home ticket from the official website (Royal Collection Trust).

There is also an option through Great Western Railway for a train/Castle combo ticket that gives you discount admission but be aware that this type of Castle ticket cannot be converted to a free 1-year pass like those bought directly from Royal Collection Trust (in person or online).

I hope you enjoy your visit!

If you take the train from Paddington Station at 8:30am you will arrive in Windsor at 9:05, and the castle is a three minute walk to the castle. As you exit the train, turn left, walk up to High Street there across the street is the castle, cross the street and at the statue of Queen Victoria turn left and walk up to the gate of the castle.

It has been several years since I went to Windsor Castle. I do remember just arriving and purchasing a ticket there. At that time, it took about 5 minutes.

I was there two years ago in June and arrived when the gates opened. There was a line but it moved quickly with no more than a 10 minute wait.