The solve page to the challenges is found by appending your solution to the shortlink stl.la. For example: stl.la/mysolution. Also, the challenges increase in difficulty from Monday to Friday. For the final challenge on Saturday, you will need the answer to each of the daily challenges to reach a solution. On Sunday there are no challenges.
Starting on March 12, 2015, an "Official Solution" for each challenge puzzle is provided at the solve page , instead of the typical story element. Later the story element returned allowing solvers to see it a bit before the rest.
Immediately below you can find the current week challenges and below it all the previous weeks with their respective theme. Here is a page with some Useful Tools.