Goodness, where to start. We go to Northumberland a lot. For the seaside Alnmouth is lovely. Seahouses is a bit kiss me quick these days, but is where boat trips to the Farne islands go from.
The little railway is the Hatherslaw railway.
Inland there is Cragside near Rothbury. It is an absolutely magnificent house with extensive grounds and gardens. There is a large play area near one of the lakes. (NT)
Wallington Hall is another stately home with a fantastic walled garden (NT)
Belsay castle has an old ruined castle and a stately home and wonderful gardens in what was the quarry.
Ford and Etal of course
Morpeth is a thriving country town and has had a lot of money spent on it recently to smarten it up.
Warkworth Castle is a ruined but fairly substantial castle. You can hire rowing boats on the river and row along to the hermitage which is open on Wednesdays (EH)
If it rains Woodhorn museum in Ashington is worth a visit. I first heard of it when Billy Connolly did a trip round Britain.
Alnwick of course, not just the castle and gardens. Hadrian's wall, Bamburgh - don't forget to visit the Grace Darling museum.
Craster - for the world's best kippers and then a walk along the coast to Dunstanburgh Castle.
Chillingham castle, reputedly England's most haunted castle.
Kielder and Ingram Valley have stunning countryside.
I absolutely adore Northumberland. If you stay away from the A1 you will still find relatively quiet roads.
Oh, and Scarborough, Whitby and Filey are in North Yorkshire.