How to create fog in one specific area of a scene rather than using volume scatter to effect whole scene Title is self explanatory. Indoor scene where you can see the outside. Fog to be illuminated by streetlights.
Instead of editing the world to have scatter volume, you can just create a mesh and place it wherever you want, then remove the surface node, and add Volume Scatter to the volume. Then adjust the Density as you want.

Hope this helps.