What do you think this is? What should I do?

Feels warm? Could be an infection or simply inflammation from the huge amount of walking. It's possible that you are just curling your toes during your stride or you have tight flexor tendons, which would curl the toes involuntarily.

Keep an eye on the redness and swelling. If it spreads, get to a doctor.

I have to wonder about all the walking though. 20km per day? Even at a really fast pace you're walking for over 2 hours every day. More likely that you would be doing around 3 hours a day. It's a respectable fitness plan if you're trying to get in shape, but you need rest days and some half days to give your body (especially your feet) a chance to recover. The last thing you want is a stress fracture or cellulitis or something to sideline you more weeks or months.