Uphill walking raises the effort without requiring you to run. Flat walking is easier to repeat, easier to recover from, and often the better base for beginners. A useful routine can include both.
What changes on a hill
Inclines demand more from the calves, glutes, breathing, and balance. Pace usually drops even though effort rises. Comparing hill and flat sessions by speed alone therefore gives the wrong impression.
Why flat routes remain valuable
Flat walking makes it easier to accumulate time and steps with less fatigue. It suits recovery days and people building tolerance. If hills aggravate pain or leave you unusually sore, return to level ground and progress more slowly.
A simple progression
Begin with a mostly flat route. Add three to five short hills, walking easily between them. Increase either the number of climbs or their length, not both at once. Use perceived effort rather than trying to preserve your flat-ground pace.
The Walking Calories Calculator gives a general estimate but cannot fully account for terrain. See also walking pace for exercise, walking-shoe considerations, the beginner plan, and Start Here.