To make bushwalking (especially the hilly steppy bits) easier and much more enjoyable, I need to do cardio workouts at the gym. I aim for 4 sessions a week, usually get in 3
I do treadmill on incline (level 15 - 20 depending on how I go), interval type stuff. I don't run, just walk fast, somewhere between 6.5 to 7 km/hr, depending on my energy levels
20 - 30 mins only, but I'm sweating by the end of it.
I'll usually do 20 mins on the bike too, sometimes some rowing
Swim afterwards, if it's not peak kiddy lesson time
Out of the gym I might go for a walk in our hilly town a couple of times a week - more in summer when it's not so cold in the mornings.
And then I have my weight circuit, especially to build up my quads. Before I was fit I had some horrible days after a rocky bushwalk, with jelly legs during, and completely sore and seized up afterwards for a few days.
It's so much better now
Basically, I don't walk to get fit, I get fit to walk