You should be in relatively decent shape to take this on because it is a hike. Wear sturdy shoes and bring water. The hike is well worth it for the photo opps. You can use the money you saved on the cable car to get a beer at the top.
I took the cable car up and then hiked down. The switchback path lets you out on a main street where the "Welcome to Dubrovnik" sign is. It is roughly 8-9 km to the Old Town from there, but you will have to go down several more staircases.
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