How to Reach the Puzzle House in Professor Layton and the Diabolical Box

There is no "Puzzle House" location inside Professor Layton and the Diabolical Box. You may be confusing:

• The Puzzle Master's House: Unlocked after completing the main story and solving all 138 (DS) / 153 (mobile) main puzzles. Accessed via the "Bonuses" menu. Contains 3 ultra-hard final puzzles.
• Layton's Challenges (Weekly Puzzles): Downloaded via Nintendo Wi-Fi Connection (service ended). Now unavailable officially.
• A Different Game: Professor Layton and the Unwound Future has a "Puzzle Battle" mode. Layton's Mystery Journey has daily puzzles.

To access the Puzzle Master's House in Diabolical Box: Finish the game, solve every main puzzle, then check Bonuses → Layton's Challenges → Puzzle Master's House.