Clockwork Castle is an unlockable board in Mario Party 6. You have to pay 100 stars at the Star Bank to play it. There were four areas that made up the board: the courtyard, Brighton's Temple, Twila's Airship, and the castle itself. Warp Pipes were on the top and bottom parts of the board (three on each side) that warped players from that side to the same colored pipe on the other side.
Landing on a ? Space near the pipes on the bottom side randomly changed the colors of the pipes, so that they also changed where players ended up when they were used. Landing on the ? Space at the back of Twila's ship gave players a chance to get an Orb by using a fishing rod to fish it out of the clouds. The ? Space behind Brighton's Temple summoned a UFO that took the player back to start. The ? Spaces that were in front of the entrances to Brighton and Twila's homes gave players a special present to the players (either coins, or a Star). Who gave them out depended on the time of day. And the ? Space at the top of the castle (board) gave players a chance to change the time of day (but there was always a 50/50 chance that it would change)!
This board got the most out of the day/night system. At daytime, players went around the board clockwise, Brighton gave out gifts when someone landed on his ? Space, the red and green pipes were active on both sides of the board, and Donkey Kong traveled around the board giving out stars to players that got to him (or he got to them). Every time all the players took their turn, DK then took his own turn by rolling the Dice Block (or two if he ate a banana) and landed on another space, making that the new Star Space. During the night, players went around the board counterclockwise, Twila gave out the gifts if players landed on her ? Space, and only the green pipes were active. DK was also replaced by Bowser. He "awarded" players that got to him (or if he got to them) with a Shadow Star that took away a Star or 20 coins if they didn't have a Star. Every time all the players took their turn, Bowser then took his own turn by rolling the Dice Block (or two if he breathed fire) and landed on another space, making that the new Shadow Star Space.
Clockwork Castle is one of the more challenging boards in the Mario Party series.