Mt. Oyama in Isehara, Kanagawa is about halfway to Hakone near Mt. Fuji. Easy day trip from Tokyo. During the Edo Period (1603–1867), Mt. Oyama was very popular for pilgrimages by the fun-loving masses in Edo/Tokyo.

It had many shrines and temples and mountain ascetic priests. When Edo/Tokyo's pop. was 1 million, Oyama saw 200,000 pilgrims per year. Today, there are fewer shrines and temples and pilgrims, but it's still a pleasant place to visit and less crowded than more well-known spots. The main attractions are Oyama Afuri Shrine and Oyama-dera Temple.
From Shinjuku, take the Odakyu Line to Isehara Station (about 1 hour). Get out the North Exit, and go to bus stop 4 to take the bus to the Oyama Cable stop. Google Map to Mt. Oyama