Rick Steves' podcasts for walking tours

You know what we have loved are Rick Steves' walking tours of various cities and even museums in Europe. Seems he has almost none for Portugal. I'd love to find a walking tour for Sintra--and some of the places inside Sintra like the Quinta da Regaleira, or cities like Porto, Coimbra, Monsanto, Evora.... Anyone have any suggestions for audio walking-tours for those places? Or, I suppose a live guide... although we try to avoid group tours for many reasons. Thanks for any recommendations.