The basement was undoubtedly on the first floor of the castle.
After circling around, Han Chenxing eventually found the passage leading to the basement behind a hidden compartment in the kitchen where sundries were stored.
Han Chenxing said, "Come here quickly, this part of the floor is clearly different, it's hollow when stepped on, the entrance to the basement passage must be here!"
Yu Ruoxun pursed her pale pink lips, unable to resist saying, "This is too well-hidden, we didn't notice it at all the first time we were in the kitchen."
Ming Ge came over, saw the situation, smiled, and said, "First, our previous searches in the kitchen focused on the key clue cards, now we're primarily looking for the basement, so naturally, we prioritize differently and the chances of finding it vary."
"Second, if it weren't well-hidden and we found 'the castle's biggest secret' right away, wouldn't the game be over as soon as it started?"
...That's true.
The group thought to themselves.