Four sliding stairs lead forward along a path to a glowing white doorway.
A ProximitySensor routes to four TimeSensors, one per sliding stair. Each stair's timer routes to a PositionInterpolator that outputs varying positions side-to-side along the X axis. The PositionInterpolator's positions are routed into translation fields for Transform nodes surrounding each stair.
By using different starting positions, the four stairs are made to slide back and forth in a pattern.