This coming Sunday I'd like to try to solve some CTF challenges, just for training. I'm a beginner, and I'm looking for people to try it out together - it's more fun and together we can do more.

There are many CTF training resources available on the Internet:  http://captf.com/practice-ctf/
In particular, this one is good:  https://picoctf.com/
And this:  https://www.root-me.org

If you are interested, feel free to join, I'll be at the hackerspace from 14h until 17h!