I used to go to Ceuta around 30 years ago when I had to leave Spain every three months and get my passport stamped to show I had not overstayed the three permitted months. It was the closest exit point to the Costa del Sol and I would walk into Morocco at the border post and then come back in the other side and ask for a stamp in my passport. I haven't been there for many years.
There is an interesting cultural mix in the little colony. I was really surprised not find anything about Ceuta in the first three guide books on Spain I looked at. This is probably because Morocco thinks Ceuta should be theirs and Spain won't give it up. The editors of the books probably don't want to upset anyone by saying Ceuta belongs to Spain.
Many sub Saharan African refugees periodically try to cross the border fence to gain entry in Europe. The Spanish government will not let any successful border jumpers cross the straits into Spain so they are stuck in Ceuta until they are unwillingly repatriated so you have this population along side long term Ceuta residents and the Moroccan traders who have bribed the corrupt Moroccan border guards to let them bring their goods into Spain.
If you have a couple more hours to spare you could go to Tetuan from Ceuta, a Moroccan village about 20kms into Morocco, sharing a taxi but I think you will find enough Moroccans in Ceuta not to bother going out of Ceuta.
Every time I look for ferry sailing times it is a struggle but google "ferrysavers.es/ceuta-ferries.htm" and try your luck. There are a least 1o sailings a day in both directions between Algeciras and Ceuta between the two ferry companies that operate this crossing.
I wouldn't bother to book the ferry tickets in advance, just turn up 30 minutes before the sailing time and get your ticket from the ticket office on shore. (By the way, have you spotted that the ferry in the picture is actually the ferry from Tarifa to Tanger?)
The 11km sea crossing itself is enjoyable and you get a great view of Gibraltar as you leave the Algeciras port and the straits of Gibraltar as you sail across. You can see everything on foot. Visit the market, the tiny beach and look for Moroccan food restaurant for lunch. At the end of the day you will definitely feel you have been somewhere different.
Although you are not technically leaving Spain, take your passport for identification purposes.
You will need to get to Algeciras, if you are going by bus from anywhere along the coast, so check out the bus schedules to Algeciras from where ever you are. The Algeciras bus station is right in front of the ferry port. If you are driving down, there is ample parking in front of the port.
Normal travel precautions apply, watch out for your belongings at all times. Keep your passport and money out of sight and reach at all times, especially if you are in a throng of shoppers or leaving the boat. Pick pockets frequent ports and prey on travellers when boarding or disembarking or congregating in queues.
If you would like to taste Moroccan food closer to home at very reasonable prices then try the Al Manar Moroccan restaurant in Marbella, it's the real thing and worth a visit.
Have a great outing whether you are eating in Morocco or in Marbella!