I guess it's a fairly common kind of experience, but somewhere around the late eighties I spent about a week on holiday in northern England, which basically meant playing arcade games in a hotel waiting for the rain to stop.
I remember this one game which started off as a standard sci fi style vertical shooter. However, you could pick up a drop which allowed you to fire a bomb which blasted a hole in the ground. When you flew over the hole you went through it and the game switched to a horizontal shooter under the ground or sometimes underwater. You could then surface through the top of the cave to switch back.
I remember it being amazing, but I was about 12, so who knows. I'd love to track it down. Anyone remember something like that?
Sorry if it's some really famous game that I deserve to be hung for not knowing
