Hin Khao Ngu Stone Park in Ratchaburi is a true hidden gem basically no one knows about, only 1.5 hours by train from Bangkok.
GET HERE:
Take the direct train from Bangkok to Ratchaburi, and from there it is only a 10 min drive to the park. You can easily ask a grab or a tuktuk to take you or rent a scooter and drive yourself. There is also public transport that goes there: Bus route Ratchaburi-Suan Phueng or "ค่ายบุรฉัตร" from Ratchaburi. Tell the ticket collector khaongu "เขางู".
Since Hin Khao Ngu Park is not far from Ratchaburi city you can also rent a bicycle and cycle there!
Can be done as a day trip from Bangkok if desired, or you can stay overnight in Ratchaburi. This is what we did as we stopped here on our way south. Ratchaburi turned out to be a surprisingly nice, authentic and clean town so I can definitely recommend staying there for a couple days and visit the nearby Heaven Valley too!
WHEN TO GO: I’d recommend going for SUNRISE to have it all to yourself or for SUNSET. Can be done midday too but it might be hot and slightly crowded with local tourists.
ENTRY: Free to visit
TIME NEEDED: 1-2 hours. The place isn’t very big but it's gorgeous so you'll probably stop to take lots of pictures. You can also rent paddle boats for 50 thb (daytime).
Don't forget to visit the secret corner of the park called "Phu Pha Raet" on Google Maps! We didn't know about it but a local recommended it later on - so go and check it out for the both of us!