The #ProjectEuler100 Challenge: for the "Dark Souls" of Coding Achievements. https://www.freecodecamp.org/news/projecteuler100-coding-challenge-competitive-programming/
Project Euler is a website created back in 2001. It hosts a collection of around 600 different algorithm problems that get progressively harder, to the point where even people with math PhD's still struggle with them.
This said, the first 100 problems are totally do-able by a new developer. Thousands of people have completed the first 100 Project Euler problems over the years.
It's just brutally hard. Like... Dark Souls hard.
Here goes solutions to the problems on Project Euler.