ATENEA CCN-CERT
I just registered to this website. It releases challenges regarding cybsecurity you can complete and test your general knowledge. It has multiple categories so you can try challenges ranging from OSINT to forensics, maybe cryptography or reversing and many more.
https://atenea.ccn-cert.cni.es/home is the link you can go to and register yourself. Spain National Cryptographic Center maintain this site.
I will be trying to solve some of these from time to time and see if I can have some fun with them.