Go to the Mordant St. NY. Follow the paths until reaching a room with a lever. Pull the lever and the lights will turn on. Enter the elevator and go up. Go find the door, then look for a brown patch on the floor. Jump as far as possible, then jump again. If you fall through, use the bear to warp there and try again you need the floor that falls for the second jump.
Dreamcast and PC Locations:Edit
Not in the Dreamcast version.
In the PC version you can unlock it as a debug option see Debug Menu.