TryHackMe guided CTF rooms, perfect for day one
→ tryhackme.com | Free tier available

📦 HackTheBox harder machines, closer to real pentesting
→ https://hackthebox.com | Free tier available

🚩 PicoCTF beginner CTFs made by Carnegie Mellon University
→ https://picoctf.org | 100% free, no setup

🌍 CTFtime.org calendar of live CTF competitions worldwide
→ https://ctftime.org | Find competitions by skill level