Spain and Morocco

The modern mosque in Casablanca - an architectural marvel and at one time the tallest building in Africa. Not much else.
Tangier is (or at least, was) a bit down at heel - just have a wander through the souks.

The Casablanca of the movie only existed in Hollywood! It’s now a large industrialized city. Note that non-Muslim’s can only visit the Casablanca Mosque as part of a guided tour. Normally all mosques in Morocco are off-limits to non-Muslims.

Rabat the capital of Morocco is only an hour away from Casablanca by train or bus and will give you a much better feel for the country with beautiful gardens, an historic area with ruins of an old mosque, the Medina etc. if you Google tours Casablanca to Rabat you can get an idea of what tours and excursions are available and see if the work within the time constraints of the cruise.

I'm not sure what "down at the heel" means, but I think Tangier has in the past had a reputation as a seedy and semi-dangerous place to wander about, with super aggressive merchants, pickpockets, and other unpleasant things.

But I was there this past February, and it's clear the government has done an amazing job of making Tangier very pleasant for visitors. Yes, wander the streets of the medina and just soak in the delightful character of the city.

The Jewish cemetery, which is just outside the walls of the medina, is interesting to visit. Also just outside the walls is St. Andrew's Anglican Church. I didn't visit, but others in my tour group did and seemed to have a positive impression.

If you have time and interest in getting away from the medina, Cape Spartel is the location where the Atlantic Ocean and the Mediterranean Sea meet. There's a lighthouse there and a signpost popular for selfies.

Both places rank very low on the list of great places to see in Morocco.
At the top of the list
Marrakesh
Fes
Rabat

The Mosque in Casablanca is about the only thing to see there.