Sevilla to Tangier to Lisbon

The usual recommendation here is to avoid Tangier day trips altogether:
- Transportation takes hours
- Many, many touts if you travel alone, "shopping stops" if you travel guided
- Tangier itself is not Morocco's best asset, far from it. I still think it is worth visiting but only as an overnight stay during a broader tour of Morocco, and perhaps not as a first visit to Morocco.

If you want to spend time in a lovely coastal city before flying to Lisbon, try Cádiz.

If you had a few more days, I'd suggest flying to Fes or Marrakech. Tangier is not a great destination and going there from Seville will chew up a lot of time for what you get. There are flights to Fes and Marrakech from many European cities, so you can include some time in Morocco during a later trip to Europe; you don't have to settle for Tangier just because you're in Spain this year.

I agree that Cadiz would be a worthwhile stop. Vejer de la Frontera is a viable day trip from Cadiz by bus. I haven't been to Jerez, but there are horse- and sherry-related activities there. I also liked Malaga. Alternatively, Rick's tours never allow enough time in major cities for me, so I know I'd be happy to spend the intervening time in Seville and/or Lisbon.

Thank you so much for the information. We have decided to spend some extra time in Seville, and perhaps take the train to Cadiz for the day.

I believe you'll be very happy with that decision.