Siblings and I were given Castle of Doctor Brain at too young an age to make much progress. It took a long time for us to figure out the puzzle on the door to get into the castle, but it must have had some strong appeal for us to keep coming back. We got stuck plenty of times after that too.!
Looked it up for nostalgia and found we must have been inadvertently been playing on a harder difficulty. Feel somewhat vindicated. https://strategywiki.org/wiki/The_Castle_of_Dr._Brain/Outsid...