Just giving a shout to my buddy Brennon. He's put a lot of work into this book.

It's a really great learning experience and taught me a ton. If you're reading this, you've probably seen me write about it already.

He made it free recently, and it's a really great book for improving your tunnel-fu: https://github.com/opsdisk/the_cyber_plumbers_handbook

He sells the labs, too. Those are a great resource if you don't want to have to do your own setup. It comes with a lab guide to help you get set up. It's $20 and you get 28 days. Not a bad deal: https://opsdisk.gumroad.com/l/cphlab