NCL Pearl, docked at Pier 35, on the Embarcadero, San Francisco, California, US.
San Francisco is an excellent town for a walk or a run, with many sights within blocks of the pier. Pier 39, the famous tourist area has many shops and restaurants. Ghirardelli Square, a shopping and dining center is also a short walk away, depending on which pier your ship docks at.
Or, go long, like I did, and walk across the Golden Gate Bridge, follow the road down to Sausalito, and take the ferry back to your ship. I did catch a city bus for a couple of miles, but you marathoners (or even half marathoners) could run the whole way.
There are endless possibilities, check below for some options.
Pier 35 to Golden Gate Bridge, Sausalito and ferry back. (8.3 miles, or less if you take the bus to the Golden Gate Bridge Welcome Center.)
Walk or run the Embarcadero.