Definitely walking. Pick a route, either walkable from your home or accessible by car or public transport. Might it take in a beauty-spot or a cafe or pub? Taking sandwiches and a flask is really nice too. DP likes gathering wild bouquets of branches and grasses for our mantle piece so this is a nice focus for a walk every few weeks.
Foraging is also really fun if you have access to countryside. There are foraging groups on FB where one can sometimes find out about local guided foraging walks.
Or, if finances and your weight permit, book a hack at a stable or equestrian centre. We've done this a few times and it's a gorgeous way to get into nature.
Alternatively, you could book yourselves in for an evening / weekend course at a local adult / further education centre together. There is usually a great variety on offer, some which run for just a day, others for a term, yet others for a year: local history lectures with field activities, Korean cuisine, botanical drawing, beginners Spanish, bicycle maintenance.
A fish monger / butcher's local to me is offering day workshops on how to prepare and cook organ foods, how to make sausages, and how to make niche condiments and sauces for a variety of meat and fish.
A book club is a really nice thing to do with a partner. It is lovely to read novels together/ to each other too.