You can do three things through exercise that actually change the appearance of your body:
- Increase muscle mass and size
- Decrease body fat (both subcutaneous and visceral)
- Improve your posture
Non-appearance related benefits are:
- Increased functional strength
- Increased cardiovascular endurance and heart/lung health
- Increased bone density
- Better joint mobility/flexibility
For a general, non sport-specific exercise programme, you generally want to strike a balance between increasing functional strength (which will also result in increased muscle mass, bone density and some fat loss), cardiovascular exercise (for fat reduction and improved cardio health), and joint mobility.
It sounds like you have the cardio covered with swimming and hiking - the key is to ensure you are making some hard (VO2max) efforts in addition to the steady state stuff. So in addition to regular pool laps, try doing some interval training - for example 100m at full speed with a minute rest between each interval. Or if hiking, push as hard as you can up hill, and try a light jog on the flat/downhill sections. If you are in the VO2max zone you should feel very uncomfortable, hot, sweaty, and unable to speak - it's something to aim for and only do in brief intervals until you are really used to it though.
For strength training, you could go to a gym, but if you have good proprioception (body position awareness) you can do everything at home. Personally I do a mixture of kettlebell exercises and callisthenics (bodyweight exercises) - you can learn how to do all these from youtube. Kettlebells and bodyweight are really good as they are functional (reflective of real-world movement) exercises, whereas most gym strength exercises (barbell and machines) don't rely reflect movement patterns that you use in real life. Functional strength is really about strength endurance rather than pushing the biggest weight you possibly can just once, which is why kettlebells and bodyweight exercises work so well - you are generally using moderate weights but doing a lot of work with them, rather than just lifting massive weights for a handful of reps and then having a big rest (which is what pure strength athletes do).
For mobility, you can't beat yoga or pilates - again, if you have reasonable proprioception you can learn to do these at home - the Down Dog app is good. You can also incorporate mobility into every day activities - for example always squat where maybe you might be tempted to bend down, e.g. when picking something up.
It's also great to combine exercises and do them spontaneously - so if you are out for a walk and you see a handy looking tree - then climb it! Or if you find a steep bank, try doing some hill sprints up it. Or if there is a log, then maybe try and do a lizard crawl along it. These kind of spontaneous outdoor exercises, in my opinion, are far more valuable, and far more fun, then sticking to a programme in a gym.