Colón sits on the Caribbean end of the Panama Canal and is the country's second-largest city, though it wears its status roughly. Much of the centre is run-down and can feel unsafe, especially after dark — take local advice and be sensible about where you walk.
That said, Colón has practical value for travellers. The harbour is a starting point for boat trips to Caribbean destinations including the San Blas Islands. The Colón Free Zone, the largest free-trade zone in the Western Hemisphere, is a curiosity if not a tourist sight. And the nearby Gatún Locks offer a close-up view of container ships transiting the canal. Most visitors pass through rather than linger, and that is probably the right call.