I could see a lot of people on HN enjoying rock climbing. Each route you climb is essentially a puzzle to solve. It's very easy to get started and you can either do it on your own if you stick to bouldering, or you can top rope or lead with a partner.

You can choose how deep down the rabbit hole you want to fall, as it can get highly technical and it's also a great opportunity to go climb outdoors on weekends.

Another striking contrast I've found in rock gyms is that there's a greater sense of community and camaraderie. I've had strangers point out where I was going wrong on a particular route, advise me on my technique, and let me borrow chalk/tape when I was out.