A short walk from New Hartley takes you to St. Mary's Island which you can find in any book on Northumberland. The causeway is covered at high tide and many are the tales of unsuspecting visitors being caught out and having to spend about 6 hours waiting to get back. I used to go to school with a girl who lived on the island and she often rowed herself to and fro in a small boat.
It's a good place for bird watching - we came across several people with binoculars. ..... Now it's back to making a few Christmas stockings!