This is the easiest and most straightforward way to increase the intensity of your walking: walk faster. I know, I know, it seems obvious, but there is a specific way to do this to get great results. Don't just "walk as fast as you can for as long as you can.
Walking up a hill is a great way to increase the intensity of your workout in a safe and gentle way. It's also good for your posture because it encourages good walking mechanics and foot striking, and it works the muscles in your hips and hamstrings.
Weighted vests are great for any walking workout. By adding some light resistance, you can strengthen your muscles, bones, and joints without putting too much pressure on them.
Adding bodyweight exercises every few minutes is another way to burn more fat. This makes your walk more of a "total-body" workout than just a boring stroll around the block.
Even though walking seems easy, it's important to warm up your muscles and joints before any exercise, especially if it's cold or wet outside.
Walking on a paved sidewalk is one thing, but walking on a natural trail with natural ups and downs and different types of ground is quite another.
Last but not least, walk longer to burn more fat and improve your cardiovascular endurance. This will help you lose more fat. Also, as you get tired, your muscles, bones, and joints work harder, which makes you stronger and more able to handle stress over time.