day trip to Versailles

Train - could not be any simpler. RER line "C" along the left bank.

Thank you it does look easy RER C but wondering about getting a pass the line benefit of having a tour guide from a service.

We did it on our own and were able to take our time and not be rushed. That was the main reason for not taking a tour. If memory serves correctly, we took the RER and it was easy-peasy. Did not have to stand in line since admisssion was part of some kind of "pass", but don't remember which one and things have probably changed since them.

Is the King’s Apartments tour still an option? A few years ago we could reserve a time and were able to wait in a comfortable sitting area with no lines. We thought it was well worth the few extra $/€ for sure. As for transportation we easily did it ourselves but at some point had to purchase tickets at an unmanned station where a dispensing kiosk was the only option. A Japanese couple had only unacceptably large banknotes or an unusable card ? and we played banker. Probably a rare occurrence and I think there was a change in the usual connection because of maintenance but alway helpful to have different size bills and coins.

Here’s Versailles website that gives good updated transportation information: https://en.chateauversailles.fr/plan-your-visit/practical-information.

Make sure to check that Versailles Chateau website closer to your dates and, on the day when you're ready to go, check the route on, for instance, citymapper (v good app for Paris public transport, and other cities too) or google maps.
This is because engineering work often takes place on holiday weekends, and 31 Oct is on such a weekend.
But don't worry: there are three rail routes to Versailles, so at least one will work.

Just posted on another post but thought I'd quickly post here too. If you're comfortable on a bike, I'd suggest doing a bike tour of Versailles. We did ours via Boutique Bike Tours https://www.boutiquebiketours.com/versailles-bike-tour/ which was recommended by another poster. The owners of Boutique Bike Tours are also tour guides and locals to Versailles. Thought they did a great job providing interesting history/background/context about Versailles, the chateau and gardens. It made the experience so much more memorable - even my 2 teenage kids enjoyed the tour and to me, that says a lot! Such a wonderful experience and to us well worth the extra cost. The cost of the tour included train tickets to/from Versailles.

We last did Versailles in 2015 using the RER. It was easy. Also, I seem to remember that we had a guide automatically in touring the inside of the palace.