I do what I call 'kids' walking which involves normal walking, jogging, sprinting, tree climbing, branch pull ups, stretches and hill work! I've developed it over many years. It's essentially what a child would do on a normal walk - mix things up!! Like you I find just walking sometimes not enough for my body - it needs to go a bit faster, loosen up. So I might start off walking but after a few minutes turn the walk into a soft jog, then the jog into a bit of a sprint. When I'm thoroughly warmed up I do stretches - usually in the park or in the woods on a track. Simple stuff but enough of a challenge to get the juices flowing.
I may climb a tree if there's a good one available, not too high. I might then try pull ups on a strong branch. I then try some short sprints, say from one tree to a post, 50-70 yards, jogging back, relaxing, then sprinting again. I might do a total of 10 - 12.
Then I round it all off with a mix - walking,jogging, skipping, sideways skip. I usually end up walking home on the last stretch, although I have been known to sprint the last 100 yards! Depends! It's not scientific at all but it could be put into a structured regime!
I would say this is low impact exercise because I only spend a max of 45 mins at any one time, and I never overdo it!
I should write a hub! Thanks for the idea.