How Long Can You Walk?

While walking we met the friend of my sister-in-law. She's been walking with long distance. 10 kilometers might even be short for her. I'm wondering if I can ever do that. Usually on my walk, I can only do 2-4 kilometers. The time the pictures are captured during my walk, it was only around 1 kilometer.

According to my husband, he can do 10 kilometers in a day which also includes his different activities. The distance was measured through his smart watch. If only for walking exercise, he can do 6-7 kilometers. But that can make him tired.

It's good to add distance gradually each time of walking exercise. How about you guys? How long can you walk?