Build a rolling robot that can navigate through a crowd from point A to point B without bumping into people.
The input could be a known floor plan for the area, and the starting position and ending positions. The robot then does localization relative to the map, and detects people as dynamic obstacles and avoids them or waits until they pass.
This is not a robustly solved problem with good implementations, although there's good resource you can use to guide you. If you can contribute a robust implementation of this kind of behavior to some existing project (ROS or whatever) then that'd be of real value to the world.