Tarragona was founded before 500 BC
and later was a major Roman outpost called Terraco.
Now the Roman ruins are a World Heritage site.
Tarragona is about 90 km. west of Barcelona with a population of approximately 133,000. Many cruise companies will have a tour that will go there, and some cruises stop there. My company took us from Barcelona on a walking tour of the ancient walled city, and after that we were left on our own. Tarragona has quite a lot to see, especially if you are interested in history - it is a small town with a big history. In many places the 2000 year old ruins are incorporated into buildings today,
You can travel to Tarragona from Barcelona by train. The Renfe trains do this journey, and the trip is 35 minutes. The station is about 1 1/4 km. to the foot of the Rambla Nova, along the streets by the ocean left on the map beside.
I have put the walking tour of Tarragona into two parts - the map beside is the first part and the second part is the oldest part of the city called the Part Alto.
Your tour bus will probably let you off where the map says 'Entrance to the old city'. and if you are on a cruise tour the old city may be the extent of your guided tour, but it is not all that there is to see.