Heart of Portugal

Seville, Madrid, Barcelona, Bilbao, Nice

Spain and Portugal aren’t particularly well linked by public transport, so I would look at flying somewhere, which opens up much of Europe including the major Spanish cities. By way of example, flights today from Lisbon include London, Paris, Edinburgh, Berlin or Amsterdam, all of which are excellent locations for a week.

The tour ends in Porto. I would look at the wiki page for the Porto airport. There's a table listing all the airlines and destinations from there. Then I'd narrow down the choices to places you can fly home from on an open-jaw ticket. Some cities may be better than others for your purposes.

I'd also consider the time of year. For instance I would avoid much of southern Europe in summer.