The Oyama pilgrimage route, designated a Japan Heritage site, was likely designated in recognition of the achievements of Mr. Iwao Oyama. While the surrounding area is residential and not a typical tourist spot, the pilgrimage route is lined with maple trees, and benches and even nighttime lights are installed. From the parking lot, you can cross the road and approach the burial site at the very back, but the entrance is closed and inaccessible. A torii gate was visible, suggesting it may have been deified.
[Website excerpt]
Iwao Oyama (former Satsuma samurai and duke), a leading figure of the Meiji era, owned a farm of 273 chobu (approximately 271 hectares) in the Nishinasuno area, and built a villa on one corner of it. Oyama passed away on December 10, 1916 (Taisho 5), and according to his will, he was buried in this place he loved dearly during his lifetime. The burial site was created in a corner of the farm that Oyama had established.
Subsequently, from the end of December of the same year to 1917 (Taisho 6), the approach to the shrine was renovated according to the design of Naosaburo Yamamoto, an engineer of the Imperial Household Ministry, and various trees were planted on both sides of the approach. Cypress trees were planted north of the Otawara Road (approximately 100 meters), while maple, cherry, and azalea trees were planted south of it (18 meters wide, approximately 200 meters long). Maple and cherry trees were planted alternately, but the cherry trees withered and were cut down.
This section of the approach south of the Otawara Road was donated to the former Nishinasuno Town by the Oyama family in 1955 (Showa 30), and has since been known as Oyama Park.

There's a free parking lot next door, and the park has playground equipment and swings for toddlers, making it a convenient place for families with children.
The area across the road seems to be the approach to the shrine, and I imagine the scenery would be very beautiful in spring and autumn. I'd like to visit again during cherry blossom season.
However, one thing I found a little strange was that the area where the playground equipment was installed was labeled "Shrine Approach."
One disappointment was that you have to cross the road to get to the shrine approach, and the pedestrian crossing is a little far away. Although the traffic isn't heavy, I felt it was a bit dangerous.
While staying in Nasushiobara, I happened to see a program about Iwao Oyama on NHK and learned that he had a burial site and a second home, so I visited them the next day.
There was a toilet and parking lot in a corner of the park.
From there, I crossed the road and walked along the gravel path to the gate of the burial site, surrounded by cedar trees, but the gate was closed, and I could only see a small part of the tombstone.
A little further on by car was the Oyama Memorial Hall, another second home, and luckily the gate to the grounds was open, so I was able to see the exterior.
The approach to the tomb of Iwao Oyama is approximately 350m long, and the maple trees line approximately 200m of that.
I visited on November 29th, but it felt about a week late.
The maple leaves were a bit reddish-dark and not very vibrant. Still, the gravel approach is well-maintained and there were many people strolling along it.
It's a straight path from Nishinasuno Station, and there's a large, free parking lot near the memorial monument, so it's easy to access. There are toilets, and stone benches dotted along the approach so you can relax.
There are also a few playground equipment, so small children can play there.