Snow Run is Snow Go. It is a special stage of Snow Go which can be accessed only from the secret warp room. It is level 2 in Crash Bandicoot 2: Cortex Strikes Back. The portal for the special stage of Snow Go is accessible from Air Crash. You will come across a part in Air Crash where there is an unoccupied platform in the middle of water, but it's at one of the water parts where you use the Turbo Surfboard, so you can't get to it right?
Wrong. You can ignore the Turbo Surfboard and bounce on the crates to reach the platform. Remember that Crash will drown if you fall in the water so make sure you land on the next crate.