Can't say it better that's San Juan
Ok here is the deal
mostly Old San Juan is for walking and there are streets where you cannot drive and that are close to any transportation beside the special "trolleys" the goverment provide for all I know is difficult to find a free parking, even on Carnival Destiny terminal...
Here is some info I found on one of our tour sites:
"Here are some basics to consider before you get started.
You will be walking around an old city in the tropics - it is very hot and usually humid. Wear sun screen and a hat! You may even consider carrying an umbrella for shade. Bring water, or plan to stop often to make sure that you stay hydrated. This city is on a hill - so you will be walking uphill and downhill throughout your visit. Also, many of the streets are cobblestone, and the sidewalks are uneven, so wear comfortable, sturdy shoes.
Old San Juan is a safe place to walk around. You will notice a large Police presence. They’re there to help you feel safe, not because of any particular recent “problem”. This bilingual Police force (specially trained for the Old San Juan tourist area) will help guide you on your way. If you’re lost or need directions, just ask. At night, you have to use common sense, but if you stay in the tourist areas, all is well.
Inexpensive parking is available in Old San Juan, luckily in easy to get to locations. There are 2 parking decks on the south side of the city - on Recinto Sur. There is also a parking lot past these deck, at la Puntilla (this is very inexpensive). The parking deck on the North shore of Old San Juan is under the Ballaja building, just off of Norzagaray Street. It is a smaller lot, and the only one on that side of the city.
If you are not comfortable with a lot of walking, there are free trolleys available that will take you around the old city."
I hope this help...
Also this link have some info on old San Juan tours;
I don't know if posting this site is against the rules, but I found quite a good info on it, if that's the case please just let me know to remove it.