I always walk on or across hot roads during summer, and hotter is better! If it's a hot parking lot I've even started standing for a while a few times while crossing for maximum heat to the feet. If it's asphalt near sidewalk, I'll walk on the asphalt as much as possible and only go to the sidewalk when it burns too much, but then back on the asphalt once the feet just cooled down once again for maximum heat to the feet. I also recently started walking over and standing on metal plates, so standing on metal plates burns really quick and leaves the soles really stinging for several seconds after stepping off the plate. I just make sure the plate doesn't show Electrical or Traffic Signal or anything else that may give a major electric shock if it's not properly grounded. If so-called "global warming" does anything beneficial for barefooting then it makes the asphalt hotter at lower air temperatures due to additional humidity. That's just a better way to get used to even hotter heat even sooner, even if it requires cooling off the feet more frequently during extended hot walks, making it possible for tolerating even more burning hot heat with even hotter air temperatures and in dry heat. Therefore lways maximum heat to the feet as long as I don't actually blister, for greater heat tolerance the next time I go out barefoot. That means the feet need to be red, stinging, even better if it feel like a pulse in the soles, and the best if the feet feel hot even overnight... or it simply wasn't hot enough.