San Juan was a walled city that spilled out past its walls that were anchored by two forts, Fort Christóbal and El Murro, the oldest Spanish fort in the Americas. In 1898 the US Navy bombarded these walls and breached them, although the landing came on the other side of the island. The English almost took the forts, to find out why they didn’t click on San Juan Stories. Here are some pictures of the forts and the walls that stretch between them.
You can get from the dock to the fortifications on one of the “Tourist Trolley” buses. There are three routes, they are free and do much of the hill climbing for you if you need it. With three ships in I assume they are packed. We used one leg to take us up the hill. We were using it as visitors from the other ships were thinking of going back, they left earlier than we by several hours. When we used it we saw a lot of locals using it for free local mass transit. Many of the residents of Old San Juan greeted th driver by name.