Phra Nakhon Khiri, (which I call Monkey Mountain), is a really nice historical site, with beautiful mountain-top Wat and palace. From the hill there beautiful views of the surrounding area.
Not on any major tourist path, so you can enjoy still some peace and quiet. I was the only tourist and human being there that day. Only monkeys were my companions. Going up, the steep hill, you will work up sweat, but there was a slight breeze on top to cool you down.
Phra Nakhon Khiri (Holy City Hill), is a historical park. Thailand, but locals know it better as Khao Wang, meaning hill with palace. The palace was built as a summer residence by King Maha Mongkut and was completed in 1860.
The park consists of three building groups, located on the three peaks of the 92m high hill. On the western peak is the actual palace of Chatchawan Wiang Chai.
The monkeys can be a nuisance as one French guy in my guesthouse experienced next day, as they ripped his cushioned motorcycle seat to pieces.