Lever

The Master pulling the lever with the intent of dropping the Doctor and Emma into the sewers of Tersurus. (TV: The Curse of Fatal Death)

Nauseated by the prospect of the Doctor and his companion, Emma, getting married, the Master announced that he would go back in time, buy the architect an expensive dinner and persuade him to place a lever next to where he was standing and a trap door where the Doctor and Emma were standing. He prepared to plunge them into the vast and disgusting sewers of Tersurus, warning them to prepare themselves for "five hundred miles of fear and faeces!"

When the Master pulled said lever, the trap door opened under his own feet, the Doctor having bought the architect an expensive dinner earlier. (TV: The Curse of Fatal Death)