Last Friday (26th March) I cycled to Nirayama from Mishima. I had a look on the map beforehand and there seemed to be some interesting things to the east of Nirayama station, so I went to have a look. Firstly, I went to a couple of temples near Jochi Water Park, which was the mini epicenter of the little trip. The first temple was called Kozanji Temple. This temple dates back quite a way. It was a very nice place, Mainly due to the nice priest and his wife, who gave me a warm welcome, even though I was just a stranger. I got a temple stamp and went to the next temple on my travels that day... 
Next, I went to Honryuji Temple. Not bad, and I received a stamp again, but not with the lovely hospitality of the previous temple. That said, it was still worth going to.
After this was the Egawa Residence, really close to the previous temples. This is the main draw of the area. Its the house of a famous Japanese chap, who was quite the polymath. He believed that firearms were the best way to defend the country from western encroachment. He also invented many practical machines, drew sketches and catalogued many animals and birds. A sort of Japanese Erasmus Darwin. It was quite an interesting place. It was 500 yen to enter when I went, a little bit pricey for what it was, but after the 1st of April 2021, the price of admission goes up to 650 yen, so think what you will about that.
After the old residence, I went round the corner to Jochi Water Park. You can fish there, walk around the park, play on the playground equipment etc. depending on your age, but the main reason I went there was to see the remains of the old castle. As I was walking through the park there was a guy playing relaxing Ghibli style keyboard music, and some Japanese people were lying on the grass listening to it and looking at the cherry blossoms. Very nice!
The castle, what was left of it, was quite impressive. Earthworks only, but you could get the general gist of the layout, with helpful signs on the way and with a nice view of the area.
I really liked this little trip. I wasn't expecting anything much, so it was a surprise to see all these interesting places all within a hundred meters of each other.
If your going there by train, its a little over a ten minute walk from Nirayama Station on the Hakone Tetsudo line.