This is actually from the Sanctuary of Truth which sits out in a small peninsula in the Gulf of Thailand and is surrounded by a seawall. The structure you see the the shadows of looks more like a gatehouse so that boats can be launched safely as the water can be rough at times.
I took this shot on top of the gatehouse type structure. There were stairs leading up so I figured why not. No idea if I was supposed to be there or not. This being Thailand its easier to ask forgiveness than permission. Asking could lead to a whole host of other issues so just quicker to play the dumb tourist than to bother the staff who are clearly not interested in being bothered as they talk amongst themselves.