As its name implies, the train travels on a single central rail, wide enough to form a track for the cars of the large vehicle. Both on the outside and inside, the monorail is sleek, and austere in terms of colours (most of them shades of white and shades of black). The exterior of the vehicle is highly aerodynamic, and seems to consist of two or three tightly connecterd cars.
There seem to be different classes of seating aboard the Monorail cars. In "Chestnut", where the Monorail is introduced, we see William and Logan enjoying a private lounge with plenty of comfortable seating and onboard service. When Maeve attempts to escape Westworld in "The Bicameral Mind", she boards the train in a car with more public, open seating (though still highly comfortable).
The Monorail carries some onboard staff, either human or host. An example is the minor character of the Stewardess, seen attending to William and Logan while they travel to the park.
Behind the scenes