One of the saddest things I see among horse owners is a lack of quality time spent with their horses. Perhaps it’s due to the misconception that horses are only “fun” when you ride them. I firmly believe that if you want your horse to enjoy being with you, you MUST interact with your horse in ways other than just riding or doing work. Think of it this way. Would you look forward to seeing someone who only interacted with you when they wanted something from you? Or if every interaction you had with them resulted in you doing work for them? I think not, yet people treat their horses this way.
There are multiple things you can do to let your horse enjoy life and enjoy time spent with you.
A simple thing you can do is hand grazing. It can be 10 minutes or it can be an hour. This is something I do often because it's so easy. Sometimes I use that grazing time to give the horse a good grooming while he’s munching away. Please note that giving your horse a treat does not count for this since it requires no time spent.
If you have a horse who enjoys being groomed, rather than one who is sour to the experience, grooming is great bonding time. If I ride, I groom twice. I do a quick, "basic" pre-ride grooming (getting off caked mud, if any, making sure saddle and girth areas are clean, running a hand over everything to check for issues, and picking out hooves). After a ride, my horse gets a much more thorough grooming. During the post ride grooming I take my time removing built up dirt/grime (the legs can get particularly grimy), brushing out sweat marks, doing a sheath cleanliness check for geldings or a teat cleanliness check for mares, picking out hooves again, cleaning and treating any badly bug bitten areas, and doing a more thorough hands on check of the entire body. If it's summer and the horse is sweaty, then part of this post ride groom is sponging or hosing the horse off. Bath time (if your horse enjoys it) also counts.
Walking the Dog. I Mean Horse:
Another thing I like to do is taking horses for walks. I love trail riding, and they are great for horses too, but sometimes I’ll just hand walk around the trails. This is great for both of us especially if the horse isn’t a great solo trail horse. If I walk in hand, the horse gets the enjoyment of the trail but not the mental burden of feeling like he is the “in charge” horse on the trail. It’s much more relaxing for him. If you don't have trails, even just walking them in hand around the barn or pastures (if you can) works. Maybe you can let your horse explore an area he hasn't been to before.
Play is also important to the horse-rider bonding experience. Do things that are fun for your horse. Does he like playing with a big exercise ball? Shaking the life out of a JollyBall? Just running around and kicking up his/her heels? Let ‘em! (As you can see from the video, Dreamer enjoys his run around time, especially in cool weather.)
Playing with your horse, or giving your horse the opportunity to play should be a regular thing. It's even more important to do this if you horse is in living conditions where they have no pasture buddies to play with and/or are stalled often. Horses need the opportunity to kick up their heels and have fun. It's not a privilege, it's a right.
Dreamer couldn’t care less about playing with balls (I’ve tried), but he will engage in play with me. At the barn he was at previously, if he had been inside a while, sometimes I would take him to the indoor arena and set him loose. Sometimes I would go in the ring with him and wait for him to meet me when he was done running around. When he did come in, I would face him, bring up my energy and run backwards, creating a draw and inviting him to play. That always did the trick! He would tear off and run around like crazy! He gets some exercise in, I get some (rather minimal if I’m being honest) exercise in, and we both have fun! I’m not asking him to work, only to play. He gets to stop when he wants to (but if it was a really cold day and he worked up any kind of sweat, then I would make him walk around a while to cool down and dry off. This is super important to do. You do not want to put away a sweaty horse in the winter), then if the grazing was good he got to do that for a while.
TL;DR: Don't make every interaction between you and your horse work related. They deserve to have fun and experience relaxing activities with their human. Don't you want to be part of their fun and relaxation?