From the Eastern Enclosure, you can enter the Main Enclosure by passing through two gate ruins and the Nagatsubone Enclosure between them.
The inside of the Main Enclosure is a square now. You can see from there views of the city area far away and the castle area around such as the Demaru Enclosure which also protected the Main Enclosure, but it is now used as a parking lot.
You can also see the Uzumi-mon Gate Ruins which is the entrance from the Second Enclosure. It is interesting to see the stones on the steps are all cut in the shape of a triangle.
Later History
After the Meiji Restoration, Iwamura Castle was abandoned and all the buildings of the castle excluding the Main Hall at the foot were demolished. The hall was also burned by a fire in 1881. Iwamura History Museum opened in 1972 at the site of the former hall and part of the hall was also restored in 1990. On the mountain side, Ena City, which owns the ruins, recently excavated and researched them to develop and preserve them. The city aims to someday make the ruins designated as a National Historic Site.
My Impression
When I visited the ruins of Iwamura Castle, I made a mistake choosing my parking spot. I wanted to walk around the ruins from the foot to the top. However, my car navigation system led me to the parking lot near the top automatically. Therefore, I had to climb down to the foot first, then I returned back to the top. For visitors who want to see the entire ruins should park at the foot. If you want to see only the great stone walls on the top, you can park at the Demaru Enclosure, which is few minutes on foot from the Main Enclosure on the top.
How to get There
I recommend using a car when you visit the castle ruins. It is about a 20-minute drive away from Ena IC on the Chuo Expressway. There are two parking lots near the top and at the foot of the ruins If you want to use public transportation, It takes about 30 minutes on foot from Iwamura Station on the Akechi Railway to arrive at the foot. To get to Iwamura Station from Tokyo or Osaka: Take the Tokaido Shinkansen super express, transfer to the Chuo Line at Nagoya Station and transfer to the Akechi Railway at Ena Station.