In the past I was only occasionally walking barefoot, on relatively short distances, on the earthy surfaces. But I'd like to train my feet to be able to do much more - including walking on harsh surfaces such as rocks. My inspiration are the documentaries of indigenous peoples walking barefoot in many environment, including rocky ones, and the family tales, that in the past people were walking barefoot to church, even in the winter.
However, I've done today a 20-minutes walk in the city. The pavements were hot because of full sun, and after reaching home I've found out that the skin on my soles is creased and I feel pain even standing. Luckily, it seems that I'm going to get out of it even without blisters.
Obviously my feet are too soft for harsher surfaces. I should walk a lot on earthy surfaces - unfortunately most trails in the surrounding are graveled... But are there any exercises, training programs or treatments to speed up the tempo of hardening foots? From what distances should I begin, and in which tempo to increase them? Does some ointments, cold or hot showers help?