Natural Features:

* A small river: Many rivers are around 3 kilometers long.

* A section of a mountain range: A single peak or a short stretch of a mountain range could be this length.

* A deep canyon: The length of a canyon can vary greatly, but a small one could be 3 kilometers.

Man-made Structures:

* A long bridge: Some bridges, like the Confederation Bridge in Canada, are around 3 kilometers long.

* A section of a highway: A highway could be 3 kilometers long, especially in urban areas.

* A large runway: Some airports have runways that are approximately 3 kilometers long.

Other:

* A marathon race course: A standard marathon is 42.195 kilometers, but a section of it could be 3 kilometers long.

* A hiking trail: A long, challenging hiking trail could be 3 kilometers in length.

It's important to note: These are just examples, and the exact length of these things can vary greatly.