I think it's really just about spending time together. You don't actually have to "do" anything other than focus on your partner for a while. For example, if you can do that just sitting and talking, that's a good place to start.
For other suggestions, my #1 would be walking. Bonus points if it's somewhere beautiful. Others would be travel, exercise classes & yoga, gardening, riding bikes, sports like golf or tennis, shared hobbies, museums, concerts, etc.