In certain screens various secret levels can be accessed.

The top level is accessed via the curbside drop off and the parking garage.

The levels are accessed using four letter passwords, which were all real words.

In the European version, the order is strictly linear and a specific level can't be accessed if the previous ones aren't cleared.

The 11 levels of parking are accessed from Gravier Street.

This level cannot be accessed without first completing stage 12.

All levels can be accessed via a map screen, and enemies are often roaming it.

Similarly, the secret level can't be accessed if said conditions aren't met.

The second level of a bank barn also could be accessed from a ramp if a hill was not available.

Each level is accessed through 'portals' from a main world.