Think about the various possible humanoid-sized vehicles (some may take multiple passengers)—

Small:

• Scooter

Medium, All-Terrain:

• Mountain Bike
• Horse

Medium, Path or Street:

• Street Bike

Medium, Street:

• Sedan or Coupe
• Taxi
• Horse-Drawn Carriage (as Driver)
• Enclosed Horse-Drawn Carriages (as Passenger)

Large, All Terrain:

• Mech-Suit

Large Street:

• School Bus

Large, on Specific Rails

• Railroad Train with multiple Train Cars
• Subway with multiple Cars

Small Water:

• Kayak
• Canoe or Rowboat

Medium, Lake or Sea:

• Yacht with Deck and Interior
• Pirate Ship with Deck, Cabin, and Below Deck

Large, Sea:

• Submarine

Giant, Specific Ports and Routes:

• Cruise Ship, with features as complex as an entire City

Small, Space:

• Space Suit

Medium, Space:

• Space Pod

Large, Space:

• Space Shuttle

Giant, Specific Spaceports:

• Starship

Some vehicles, such as the Scooter, Bike, or Horse, are small enough, and you remain within visual contact with the outside elements, insomuch that they effectively become part of your character when you've mounted them. You are then assumed to “ride” or “drive” instead of “walk” when you use move/go commands, and may continue to traverse the open world largely as usual. There may, however, be some areas that you cannot enter with certain types of mounts, and other areas that are only accessible with a proper mount.

Other vehicles, such as an automobile or a boat, may act as an area including within themselves one or more locations which can be explored. They may still be navigated, driven or ridden, but they are limited to designated ports (such as taxi stops, streets, or harbors.)

Vehicles may also be nested: It may be possible to mount a horse, then ride it onto a pirate ship, or to enter an escape pod while onboard a starship.

If you are in a nested vehicle and location situation, “exit” may become very ambiguous, and you would need to clarify by specifying something more clear such as “exit cabin”, “dismount horse,” or “disembark ship.”