Danny-le-Ville, a walking city on Hardy who has become something of a celebrity
Several worlds have some or many mobile cities, which take a wide variety of forms.
One common design is the scrub slug, which 'float' on a layer of specialised utility fog, which is sometimes disguised with optical phased array technology to appear invisible. Scrub slugs were originally developed as military ground vehicles.
Many, but not all, of these large mobile metropolises are independently sophont, or at least very competent if not self-aware. Most fall into the category Modosophont, usually at high su-vec level. Some are low transapient entities, while a very few are S:2.