Title of children's book from the 80s-90s about a tomboy?

I read this book as a child and would love to read it again. I can't remember much, but it's about a girl who's a tomboy and always wears a baseball cap. She hates dresses and anything girly, and when her mom forced her to wear a dress to school, she cut it up and sewed it into shorts. She ends up in this strange place (can't remember if it's another world or not) and encounters an old man. I think he might have been an inventor, but I'm not sure. The only other thing I can remember is her climbing a big pile of junk/electronics during the climax of the book to get to something (maybe a key?) at the top. I know it's not much to go on, but can anyone please help me?