I found this on Google Maps, so I went there but when I got to the Entrance, the Guards wouldn’t let me in. They couldn’t speak English very well, so I didn’t know why. Maybe they had closed it already, or maybe it was under renovation. Or it may even be under attack by Aliens that particular day, who knows. At any rate, I just contented myself of taking pictures of the armed soldiers on Guard Duty around that area. Forget about visiting this place, at least if and when until they get their act together in terms of opening it to the Public.
It is located along the Ratchadamnoen Nok Road in the Phra Nakhon District and it is not very near any Train Station. Your best bet would be to go down the Ratchatewi BTS Skytrain Station and then take a Taxi to go there. I used Google Map Screenshot of the Gate with its Thai name to communicate with the Taxi Drivers. Of course, it was all for nothing, and since I am not recommending anybody to go there, then treat these instructions as just for unnecessary information.