York or elsewhere - early/mid-June

https://www.nationaltrust.org.uk/goddards-house-and-garden/features/the-gardens-at-goddards-

And absolutely go to Evensong at the Minster.
Awesome in the true sense of the word

I remember Durham as one of highlights of our trip to UK. We were driving down from Hexham and Hadrian's Wall which is a worthy destination if you have more time, and stopped at the Durham Cathedral and Castle. The Cathedral is Fabulous with every huge Pillar carved with an original design pattern. And of course you will want to pay respect to St. Cuthbert and the Venerable Bede, who are interned there. Old Town Durham is an Unesco site. The Train Liner from York to Durham, takes a little over an hour both ways, and looks like it is pretty direct.

You can easily fill at least 2 full days in York or longer if you want to explore the Viking stuff. Two nights is only one day somewhere.

Check out the National Garden Scheme - ngs.org.uk for private gardens that are open to the public.

You can spend a day in Durham and from there spend a further day at nearby Beamish Open Air Museum to see how life was a hundred years ago. Cover Hadrian’s Wall from here.

Later in June will be more colourful, but unless there is a late frost, there should be plenty of interest in the northern gardens.

I skipped some of the traditional sights in York but still enjoyed being in the city. While there I took a day trip by bus over to Whitby. Durham will be a target on my next trip to that area; it sounds very worthwhile.

Another possibility might be northern Wales. I visited it from Chester. Bodnant Garden was really impressive. It's manageable by train+bus, though the buses aren't super-frequent.

A (20th-century) historical destination you didn't mention having visited is Bletchley Park, the WWII code-breaking center. It can fill nearly a whole day if you're seriously interested in the subject. There's rail service from London on the line going to Coventry.

If you get up to Scotland on a future trip, you'll find lovely gardens at many of the castles. I'm not really a castle-interior person, but I loved the gardens. Many are manageable by bus.

I think a trip to York would be great and you could even take the train. Spend some time and around York and then I'd go to visit Harrogate by train. It has some wonderful gardens and outdoor activities and is quite close to the Dales National Park. A week up North is just what you need after being down in the Big Smoke(do they still call it that?).

heather just beat me to it - just got out of bed on Good Friday - consider a train to Harrogate from York or wherever you find yourself (33 minutes on the Leeds train provided by Northern) a lovely walk through town leads you through acres of municipal gardens (the town takes gardens very seriously in Harrogate) to RHS (Royal Horticultural Society) Harlow Carr. https://www.rhs.org.uk/gardens/harlow-carr Hard to beat, beautiful setting as well the fabulous gardens which will be in full-flow, (as an active RHS member, may be a touch prejudiced, but probably not).

There is also the North York Moors northeast of York. With a preserved steam railway taking you towards the coast. Beautiful - both the scenery and the train. Miles and miles of moors.

You may find that there is so much that appeals to you in and around York that you don't have time left for Durham.

There is an awful lot in the Northeast for garden lovers. You'll have to make a follow-up trip.

Durham could be the "vacation within your vacation". We spent one night there between York and London and loved it. There is a lovely walk along the river. We stayed at the Marriott and ate at a pizza place on the street between there and the cathedral.

Thank you all for the replies, I will extend my nights up there.
Would it make sense just to base myself overnight in York? Probably best so I don't have to use time taking my stuff with me and checking into new places. (Answering my own questions here)

7 June-- Train to York in the late morning/early afternoon - spend rest of day and overnight in York

8 June- Durham for the day - back to York for overnight

9 June- York/Goddards House

10 June- Day trip to Harrogate/possibly Harlow Carr/ back to York overnight

11 June-Morning in York/Train back to London in the afternoon

I can't decide if I should cut Durham or Harrogate out to have more time in York or leave them as day trips. I am sure that both are deserving of more than day trips. I guess I could also make that decision after I arrive and explore York some.

Have you looked at the visitor website. www.visityork.org.

I went for a few days to York a few years back and found plenty to do without leaving the city, but it was December - so not so good for gardens etc.

If its survived the pandemic, there was a tourist office in the centre, which will have lots of info. I bought a visitor pass, which allowed me access to a bunch of stuff - which was worth it for me. Not everything was on the pass, don't think the place where you make chocolate was, and - of course - some venues are free.

May not seem obvious if you are not used to rail travel, but the National Rail Museum - which is free entry - is vast and fabulous. I spent at least half a day there.

Think Durham would make a great day trip from York, as its less than an hour by train. But, can't comment on other suggestions - others here have much more knowledge about trips outside of York.

Ashley you could spend a week or more in York visiting nearby gardens let alone the sights in the city itself!
Local gardens accessible by public transport with maybe a bit of a walk include
Castle Howard
Benningborough
Scampston
Breezy Knees!
Burnby Hall (small but a brass band on Sundays too!)
Helmsley, Rievaulx and Rievaulx Terrace (could spend a couple of days here as also Duncombe Park to visit)

Not as grand but there are also the museum gardens and rowntree park within the city itself as well as the gardens mentioned by others above.

If they still offer them, the free walking tours given by local people are a must-do in York. I really enjoyed the York Castle Museum.