I only played this a few nights ago. At the time, I thought the "turn its tile over" meant the back of the target token. However, reading that now, I checked the map tiles the target tokens are placed on. It's 34a, 29a, and 26a. All of them look neat or light, and, when turned over, look destroyed or dark. Especially tile 26a turns into a pit when turned into 26b. So, I think the "turn its tile over" is for dramatic and visual effect.
It doesn't seem to change the game play. You can still enter these spaces when the tiles are turned. Also, the card says "any figures there are killed", so ghasts or any other monster there was killed when the space blew up.