I am looking for a site that publishing riddles and problems such as [Poject Euler][1] 
publishes problems in computer science. Is there any similar site that is hardcore in the area of physics? 


this [site][2] has some good problems set, but it seems like there isn't a community and sharing of solutions/ideas like in Project Euler.


  [1]: https://projecteuler.net/
  [2]: http://www.feynmanlectures.info/