Things to do
The garden is about two and a quarter acres, with a trout and salmon stream at the bottom. A lot has been achieved already. The first target was to turn the former nettle patch into rough grass, which means that there is already lots of space for sitting or strolling. Birdwatchers might spot the visiting heron and the resident kestrel. You can see more about the house and garden at www.cooper363.fr.
The valley of the Course (the trout stream) is quite a tourist attraction in itself, and offers attractive walking - and a chocolate factory!
Further afield Montreuil sur Mer (misleading name - the sea has not been there for hundreds of years) should not be missed. At the very least a walk round the ramparts offers stunning views. The town is well worth a visit, and if you are interested in good food there are two Michelin-starred restaurants and at least a dozen other good places to eat. Foodies might enjoy this website https://ladestinationgastronomique.com/fr/
There are lots of local events. Jumble sale enthusiasts will adore the enormous brocante on July 14 in Montreuil, while foodies would enjoy the herring festival in Etaples in November. There are also nearby gardens worth visiting at the Abbaye de Valloires, while further afield is the wonderful garden of Les Plumes.
Le Touquet is well worth a visit, maybe for its large Saturday market, but certainly for its quirky 1930s architecture and enormous sandy beach. You could combine this with a visit to the fishing port of Etaples, where there is an excellent museum of fishing (with aquarium) called the Mareis.
Beaches are perhaps half an hour away by car, and are all large, flat and sandy. There is sand-yachting at Merlimont and enough space for a million sand castles.
The Nausicaa aquarium at Boulogne is said to be worth a visit, as is the old town centre. The crypt of Notre Dame de Boulogne is extraordinary.
The bird sanctuary at Marquenterre is well worth the drive. For history lovers there are WWI sites to explore (don't miss the cemetery at Etaples) and near St. Omer is La Coupole, a WWII V2 launching site. Going further back the battlefields of Crecy and Agincourt are within driving distance. The Donjon de Bours is not to be missed.
Art lovers should not miss Louvre-Lens, a stunning building and great art an hour and a half away by car. There is also a Matisse museum at Cambrai (his birthplace), maybe two hours by car
Day trips can easily be made to Paris, Lille (for "La Piscine" art gallery and museum) or Arras by train.
There are also videos (in French) on Youtube. e.g. https://www.youtube.com/watch?v=GldVdBmg8Ho