I'm deciding right now what I want to do next term (final half year before going into masters)

This is how I rank my choice of bachelor project topic

1 - Robotics enhancing human strength (control theory)
2 - Privacy aware gunshot detector (app design and signals)
3 - River detection of images (machine learning)
4 - Physics engine for simple 2D games
5 - Alternate reality fiction story (web- and game design)
6 - Self driving cars (Computer science)
7 - Product line balancing (Computer science)
8 - Vehicle hacking/security analysis (IT)
9 - GPU calculation of fluid physics
10 - Augmented reality app aiding GPS navigation
11 - Generation of Wikipedia articles (Machine learning)

I feel tempted to move some around but I'm not sure... I have three criteria.

First of all, it has to be moderately difficult because I want to learn something. Second of all what I learn has to be of use for me in the future. And third, it has to be fun.

None of these tick all boxes.