Hi AL,
We have been to Northumberland many times and amongst our favourite places are (in no particular order)...
Craster - A beautiful small village and harbour with a lifeboat station and The Jolly Fisherman which serves excellent food. Parking is at the edge of the village and only a short walk away. You can also walk to Dunstanborough Castle (NT) from here.
Seahouses - Only good for fuel and driving through, unless you want sand castle buckets and 'Kiss me quick' hats!
Holy Island - A must see location but check tide times for the causeway! Lindisfarne castle (NT) is well worth a visit.
Bamburgh - A lovely village with the castle and lots of traditional shops. Car park at South of village was free last time we were there.
Chillingham Castle - Not a coastal location but an absolute must see destination!
Alnwick - A short drive inland but the castle and gardens are absolutely worth a visit.
Cragside (NT) - The birthplace of hydro electric power and indoor lighting. Fascinating house. Park in the garden car park and catch the shuttle bus around the site.
Enjoy wherever you do go and let us know if you find any more places to visit.
Keith.