Well well, my parents have a house about 20 mins from Dieppe so I know the area well. Lots to do!
I like Dieppe castle, and the cathedral’s lovely.
There’s a wonderful house and garden not far away - Le Bois de Moutiers.
At the bottom of our village there’s a weird Bison farm that has outdoor activities and camping, but also a restaurant - https://www.revedebisons.com/ - that I think its great! Not fine dining, but an experience nonetheless. Better in the summer as you sip an aperitif overlooking the valley.
Assuming you have a car get to the Val Ygot V1 bomber site that was destroyed before active but preserved as such - very poignant.
Loads of great restaurants in Dieppe itself - make sure you try A La Marmite Dieppoise! And grab a hot chocolate at Café des Tribunaux.
One of the best restaurants in the area is Le Cheval Blanc at Longueville-sur-Scie. The owners are an absolute delight. Although I am not sure if they retired, so that recommendation might be out of date! Have fun