How do I access the secret room with loads of coins? I did it once but I have no idea how.
I have 3 hours of total play/80 runs and for the first time yesterday I somehow got into a cave which had big metal doors that opened when I approached; I grabbed a magnet powerup and went into a big square room with tons of coins (I think it was a 6-coin thick row, instead of the usual maximum 3).
I did not notice going into any weird direction to access it, I believe I just followed the usual road. Is there any special way to access it (such as hitting a certain obstacle) or is it a rare event that happens at random?