In the framework of Erasmus+KA2 ROOTS/ Routes to Outdoor Oriented Teaching and Sustainability, Mathematician and member of ROOTS pedagogical team Mr S. Drosakis designed and taught an Algebra lesson in the school’s courtyard. B2 class students had wondered “what do we need Trigonometry for?” and this outdoor lesson was the answer, using the practical application of Trigonometry to measure experimentally the volume of a cylindrical column in the school’s courtyard. The lesson took place on 26/2/2019 and was followed by a discussion in order to link the textbook’s theoretical knowledge to the required experimental measurements.