3 historic towns in one day

If your keen and start early you can do the three towns - El Escorial, Avila and Segovia in one day as they are fairly close to each other.

I'd probably do it that way as ElEscorial is an hour form La Trocha, an hour there then over to Avila to walk the wall and maybe lunch , then off to Segovia.

On the way turn off the pay roads (pejaes) on your GPS and go back via the mountains (only about 10 minutes slower but way cooler)