Leeds Castle trip or join a tour from London?

not sure if you mean doing the "trip with our car" with a spare "a", or "trip without a car" with a spare space and r for t swap.

If you mean with your car it is easy on your own for a day trip. Down the motorway, into Kent, get off when the signs say so.

If you meant without a car, a train from London will get you close and you can walk or take a taxi.

Either way, no need to stay overnight unless you want, and no need for a tour.

Nice place. Have you also considered Hever Castle nearby, of Anne Boleyn (Henry VIII's beheaded wife) fame?

Sorry; we are using trains and buses, and not renting a car.
There are many wonderful castles, but my reason for Leeds is that it was part of a story I wrote for my grandson. In my story Edward and his friend Henry had an adventure there. After researching its history, I now have the chance to see it. The story took place at many castles but we will be near this one…, and it is not a ruin.

From the Leeds Castle website:

TRAVELLING BY TRAIN
Southeastern trains run frequent services to Bearsted and Hollingbourne stations. There are direct trains to both stations from: Ashford International (25-30 mins) and London Victoria (70-75 mins). It’s then a 5-minute taxi ride or a 30-40 minute walk to Leeds Castle.

A very easy day trip from London.

One potentially confusing thing - Leeds Castle is in Kent (south east of London). The city of Leeds is about 200 m north of London and, to my knowledge, has no Castle.

Leeds Castle is wonderful - especially the setting. I remember when little (and long before it was open to the public) glimpsing it from the road when it seemed the ultimate fairy tale castle and almost magical. It took another 60 nyears before I managed a visit and I loved it. Not only are their the grounds but the castle itself has so much history and was associated with so many queens of england too. It can be done as a day visit, but if possible I would try and spend the night in the castle just for the experience!

Buy tickets here:
https://leeds-castle.com/visit/
But wait until you get there to buy, if you are planning on using the 20% off offer detailed below.

Directions for getting there by GoodJourney (car free):
https://www.goodjourney.org.uk/attractions/leeds-castle/
From their website:
"Enjoy 20% off entry when you travel car-free and show a valid train or bus ticket, bus pass (with receipt) or bike on arrival (valid 7 days a week). For bus pass receipts – hold your bus pass over the onboard ticket machine reader until you see a green light or hear a beep, then take your receipt."

https://leeds-castle.com/visit/opening-times-and-directions/
"Southeastern runs frequent services to Bearsted and Hollingbourne stations. There are direct trains to both stations from: Ashford International (25-30 mins) and London Victoria (70-75 mins). It’s then a 5-minute taxi ride or a 30-40 minute walk to Leeds Castle.

GREEN TRAVEL OFFER: Show your train ticket on arrival and receive 20% off* your admission tickets."

*Train ticket must be valid for the same day of travel as visit date. There must be a physical/electronic ticket/receipt. Offer can be redeemed at Visitor Centre only.
https://leeds-castle.com/wp-content/uploads/2023/08/Green-Travel-Offer-Terms-and-Conditions.pdf

P.S. I would stay the night there, to really experience it, rather than just getting a quick look.

Thank you, everybody! I think we will ( go broke) and spend the night.

Back in 2019, I stayed two nights at Leeds Castle. It was fantastic and a wonderful experience. I highly recommend it. I don't know how much it is to stay there now, but it was very reasonable. We stayed in the Stable court Yard but you can stay in the actual castle (cost is more). The views at night from the Castle view restaurant were just breathtaking and the food excellent. We were there in June and believe it or not, one night we were the only guests in the restaurant and we were able to wander the grounds as much as we wanted with no one else in sight. It was incredible to have the place to ourselves. The gardens are wonderful. We actually had a car, but did a small day trip out to Canterbury by train. I remember on our return, there was not a taxi available, so walked to the closest pub. The landlord told us all kinds of stories about Lady Baillie and how the locals all loved her when they worked at the castle. We ended up getting a taxi from the pub to the castle.