When I was younger I read a book. I have no idea what it was called or who wrote it or what the character’s names were. All I can remember is that some kids (middle school or high school) figured out some way to, or found some device which allowed them to, enter a higher dimension. As I recall it was still our universe but there were additional dimensions (or maybe just one extra) on top of the usual three. This sounds crazy because I can’t remember enough about it to explain it correctly.
I do remember that they were able to use this dimension-skip thingy to get past a locked door. The door led to a rooftop at their school, I think. Also, one of the kids had a ketchup packet in his pocket. When he took it into this other dimension and then brought it back, then tried to eat it, it tasted like expensive chocolate instead of ketchup, or something.
I read this book sometime before I turned sixteen. This tells me that it had to have been published before 2000.
Does anyone have any idea what I’m talking about?