London-Edinburgh-Dublin

It's doable, but it's pretty nonstop. If you can survive your first day, then go for it. Sleep when you return home.

Day 8 - Dublin: Open. Choose to visit one museum and relax or split
the day with AM in Howth/Dalkey and end the day in Phoenix Park.

Strong vote for Howth. I did 2 day trips there this past May. I was not impressed with Dalkey at all. I would skip it.

My trip report might give you some ideas.

https://community.ricksteves.com/travel-forum/trip-reports/solo-in-ireland-may-2025-my-trip-report

My Dublin time was mixed in with other locations. So, you'll have to scroll to see my 3 different Dublin parts.

I feel it is too rushed for you. Just curious. What time would you depart for Edinburgh from London or Oxford? Not clear. Will you stay overnight at Oxford before departing for Edinburgh?

Wow you are physically stronger. Have you already bought online tickets for train to Edinburgh?

If your flight is significantly late you could end up struggling for time to go into London, check into a hotel and get brunch then be in Watford by 2pm. That is before the tiredness of the day from the flight.
The alternative is to take either the Rail Air bus (hourly) or the bus 724 (destination Harlow), hourly to Watford Junction and have brunch in Watford.
I have checked and the studios do have luggage storage (see their FAQ's).

Both have almost the same journey time of an hour, the 724 is 1/4 the price of the Rail-Air bus.

Afterwards train to your hotel.

On Day 2 check if the bus leaves from Victoria (Rail) Station or Victoria Coach Station. Usually the latter and they usually leave from the very low numbered stands- 1 and 2
.

Thanks all!

1) Will look into Howth!

2) What time would you depart for Edinburgh from London or Oxford? Not clear. Will you stay overnight at Oxford before departing for Edinburgh? Wow you are physically stronger. Have you already bought online tickets for train to Edinburgh?

I won't be staying overnight in Oxford. The visit is part of a day tour to all 3 places, leaving at 8AM from Victoria Station and returning at 7PM. The train from London to Edinburgh leaves at 8:50AM from King's Cross. We're in our early 30s, and trying to maximize our physicals before it all goes downhill!

3) The alternative is to take either the Rail Air bus (hourly) or the bus 724 (destination Harlow), hourly to Watford Junction and have brunch in Watford.

I didn't know about this option, thanks!

Just so you know, I think most regulars on here would advise against a day trip trying to fit in Windsor, Stonehenge and Oxford. It will be a whistle stop tour of all 3 and what you will be most familiar with afterwards will be the UK's motorway network as you will spend a lot of time travelling. I would be bothered about doing it on your second day as you may well spend much of it asleep on the coach.