Walking
The most underrated exercise there is.
No barrier to entry
Walking needs no equipment, no gym, and no skill, which is exactly why it works: nothing about it gives you an excuse to skip it. A brisk pace, where conversation is possible but you notice the effort, is all it takes to count.
Making it count
Incline is the cheat code. Walking uphill or on an incline treadmill raises the effort without pounding the joints the way running does. Thirty to sixty minutes at a purposeful pace is a full LISS session.
Zone 2 by feel
Breathing harder, still able to talk. That's the zone.
Incline over speed
Raise the hill before you raise the pace.
Stack it onto life
Commutes, calls, and errands all count when the pace is honest.