Not everything on the Underground is as it seems. After telling the world of Ten Illegal Things To Do In London, creative investigator Tom Scott sets off with "Stand-Up Mathematician" Matt Parker to unveil more mysteries. Your Tube journey may never be the same again.
Those curious to know exactly what a "travolator" is can read more here.
Want more insight into your daily commute? We have already shed some light onto the secret bits of the Northern Line and the Victoria Line.