No, this is not some weird spin on Formula 1, where the race track includes multiple walls. By wall formula, we mean the writing you see painted on many buildings, including here in Leiden. Poems and stories written in various languages are scattered throughout the city centre. However, in recent years, actual physical formulas have cropped up in between the prose and poetry. If you ever need a reminder of Einstein's field equation or Snellius' law of refraction, just stare at a wall, and maybe you’ll have some luck!