Any recommendations for routes for a walking challenge?

I am going to Japan in April '26, and as this is not my first trip to Japan I want to try something to challenge myself. So I am interested in breaking my record for steps in a day, my previous record is 26k and probably will be aiming for 28-30k. Does anyone know a good path that can cover say about 5 hours of walking on not-too-steep terrain? I will be mostly staying in Tokyo, and I guess I could walk around the Yamanote Line route as an example. But I am open to recommendations. Many thanks.