Haven’t seen anyone mention https://overthewire.org/wargames/bandit/ yet. It’s a Linux shell game where you need to solve problems using shell commands that only requires an ssh client on your machine: you ssh into the first server, solve a problem, and the solution points you to the next server. It starts easy (e.g. read out this file using cat) but gets hard quickly. But you can always look up solutions when you’re stuck. It gives a good idea what certain commands are used for and how they can be combined in powerful ways.

Ross (Accursed Farms) did a really good review/analysis of the game: https://youtu.be/rxOKEsBx4NU?si=a7UHgYa-TqCfnqvB

I can recommend this too. I got the WiFi version. Integrates beautifully with home assistant including motion/person detection.