I'd like to include some cardio or HIIT to my F1 schedule. My motivation for training in general revolves around learning new stuff (hence my fondness of F1). Therefore I'm not so good with treadmills and such.
This thread is for suggestions for cardio or HIIT that:
- Doesn't interfere with F1, which is the main priority.
- Develops new skills, i.e not boring, which kills motivation.
- Doesn't require expensive equipment. The less equipment, the better

In order not to interfere with F1, the cardio should probably involve 80-90% or so lower body work. I know that I won't personally be pushing my luck with burpees, man-makers, kettlebell clean & jerks and so forth. I like these kinds of drills, but they'll probably eat into F1 recovery - Am I wrong?
So, I'll chip in with a couple of suggestions. Looking forward to hearing other suggestions. Let's get creative!
Barefoot running:
I'll pick this up again this spring-summer-autumn. Will start very gently, and will probably end up running for no more than 20-30 minutes once a week - Any more than that is asking for trouble in my case, due to my knee. In my experience, there's a lot of skill involved. In the past, as soon as I let the form go, my right knee began to ache. Staying focused on proper form resulted in painfree running.
Jump rope:
There's so much skill, coordination, endurance to be learned here, it's just unreal. 10 minutes of intensive mixed skipping after F1 would probably work magic on one's conditioning. Skipping also has much lower impact on the joints. The rope is easy to pack for travelling, as well.