Heathrow hotels to Windsor

I looked up the hotel address. It is, like many Heathrow hotels, on the Bath Road which runs along the north side of the airport. It is not near any terminals or any railway stations. If coming from any of the Heathrow terminals, you will need a taxi or shuttle bus to reach the hotel.
You will also need a taxi to get from the hotel to Windsor. Buses to Windsor run from the terminals.

Hotel website here: https://www.parkinn.co.uk/airporthotel-heathrow

Taxi would be the easiest, it’s a 15 minute drive to Windsor.

That Bath Road does have bus stops right along the way, and you can get on regular local buses with an Oyster card, but they change in Slough to get to Windsor (2011), and when I did it, the other connecting bus never showed up and I ended up calling a cab anyway, so I could meet my boyfriend from Maidenhead (who also turned out to be late).

Yes, taxi is fine, not that expensive, I took one from Windsor to Heathrow in 2015 no problem. I don't recall exactly what it cost, might have been £25 ? Something like that. Your hotel should be able to tell you how much a taxi will cost to the Castle, so you'll know for sure. It's coming up as 9 miles on Google Maps.

I went on the hop-on hop-off bus tour of Windsor and Eton, we went to the Windsor Farm Shop that Prince Phillip developed, we still have the tote bag with their logo that my daughter bought :) Honestly, I would not do that tour again, it had a lot of countryside with no sights, seemed not to be a very direct route, but at least it got us over to the farm shop. Bought a pasty. And a tote bag. Did what was required of us :) Got to see Eton again. Better than walking.

Taxi, right to the castle, you should be good. Yes the pub right near the gate is very good, authentic. There are also very good restaurants in the shopping area across the street, for surpisingly good prices. We were there in Sept and there were great sales in the shops too.

Best trick for the whole visit was that I had bought a little monocular, half of a binocular (lighter), the telescope maker Celestron makes them, GREAT for Windsor Castle. So many details and towers, gardens, etc., to see outside, and having a more close-up view really helped. It was so big on the INside that I could use it there too, giant paintings with name plates that you can't read unless you have some binoculars :) We also have a few Knights of the Garter in our family tree, so we were able to find his crest on the ceiling and his name on the wall, and take photos once we knew where to point the camera.

I also heard a guard explaining to a tourist that he was not allowed in late in the day because he did not buy his ticket directly from their box office, but from another service like the London Pass or something. So if you do run late, be sure you're getting your ticket directly from the castle.

Have a great time!
-Alison