Make a list of five forms of mass transit. Buses, ferrys, trains, planes, wagon trains, whatever. Multiple people involved.
Next, make a list of five types of people you might see there who might stand out to you. Nuns, salesmen at a convention, a rock band complete with entourage.
Finally, make a list of things which people cannot physically do. Flying, slithering across the ground like a snake, shedding their skin, snuffing out the sun with the thumb and index finger.
Now, mix these all up and grab a trio. Put yourself in that place and observe them doing the activity. Imagine them partaking in it. See what happens.
See Anne Sexton watching nuns on a ferry here.