Question Dubrovnik Walls Tour - Worth It?

We're stopping in Dubrovnik during a cruise this May, and I'm considering a tour that includes walking the famous walls. Has anyone done this? Is it as breathtaking as they say, or is it just another tourist trap? Also, how strenuous is the walk? We're not exactly fitness buffs, so I'm a bit concerned about whether we can handle it. Any advice or tips would be super helpful!