I have found that with research, Ricks books, and audio tours there are many sites you can see on your own perfectly. However there are some sites that just go faster with shorter lines or that the experience is just greatly enriched by going on a guided tour or hiring a private tour guide. Of these cities are there tours or sites that we should get a guide for sure?
And if you know of some great experience please share that. Our food and cooking tours elsewhere have been a blast as well as we enjoyed guided tours at some historical sites and at least one museum especially in Italy for better access and info. But others we were fine on our own. Time frame April and May. Two experience travelers. These are the cities
Seville, Córdoba, Grenada, Barcelona ( also if you want to chime in about Porto and Lisbon)