Easy walking has worked well for me, especially when my legs are sore. I wouldn’t call it cardio though. Just moving around and getting some blood flowing without turning it into another stressful session.
Some good points here. I think I’ve been overthinking rest days a little. I’m gonna keep the easy walking and mobility when I feel good, but if I’m completely smoked, I’m taking the damn couch day without feeling guilty about it. 
