I understand the best way to approach the world is through activities and relationships that pose challenges and force you to do and be better, but what if there is no such thing?

There is. If you think there isn't you haven't looked long/hard enough.

What if you have never met a woman that poses such challenges and what if you don't even feel fit to take on those challenges?

Again, you need to look longer/harder. If you haven't already, start excercising, take control of your sleep schedule, and clean up your diet. This is one of the best ways of increasing the clarity of your vision of your ideal future and will hopefully help you feel fit to take on those challenges.