How long does it take a human to walk 100 kilometers?

The average walking pace is 3-4 miles / hour, so you're looking at 25-33 hours of solid walking - if you're able to do it in one go.

Depending on your speed or athleticism.

Lets say you're walking 1 mph, then it will take you 100 hours.

if you're walking 1 mile a day, then 100 days,

Also,you may not maintain the same speed through your walk, so it might take more time.