Tres Cantos separates from Colmenar Viejo Historical milestone · Tres Cantos, Área Metropolitana, Madrid Image of Tres Cantos, not of the place itself. The city, planned in 1970 as an urgent town-planning operation to decongest Madrid and inhabited since 1982, became the youngest municipality in the region on separating from Colmenar Viejo by regional decree. 21 de marzo de 1991 Photo: Yoalex41 (CC BY-SA 3.0) What to see and do in Tres Cantos