When I was much younger I played a midieval based board game with a portal in the middle and towers I think around the perimeter. I remember that once someone entered the portal in the middle there was a limited time to get to the center before the entire board flipped over around this portal. For the life of me I cannot remember the board game title or who even made it. The year would be 1993-1995. I know this isn't much to go on. I have searched this forum for keywords and I have spoken to several board game business employees and they seem to be either to young to know or they just don't know.
Also, if it helps I believe that the game had some plastic insert features similar to the fashion that were in life. They fit into the board after unfolding and assembling. I know that the board was very large in size too. Thanks for investigating with me!