Featured on the cover of the April issue, Mimei Thompson’s fantastical cave painting reveals the strata sedimented into our planet’s rocky crust, striped through with minerals and other richnesses and beckoning us further inside. Far from being a blank or inconsequential space, the underground is a critical and contested site, full of foundations, infrastructures, and junk; hidden architectures tucked neatly underneath the surface. Excavated, extracted from, dug up and bored through, the underground is made messy so that things on the surface can be kept clean. This issue, we peel back the skin of the earth to look at what goes on under.Keynote: core beliefs, Maria de Lourdes Melo ZuritaBuilding: Metro station in Santiago, Chile by Beals Lyon Arquitectos, Pedro Ignacio AlonsoFuture archaeology, Manon MollardCase study: Deltawerk 1:1 in Waterloopbos, the Netherlands by RAAAFCase study: Subterranean public space in Groningen, the Netherlands by RAAAFCase study: Ca’n Terra in Menorca, Spain by Ensamble StudioUndermined planet, Rania Ghosn and El Hadi Jazairy of Design EarthBuilding: Arzo quarry park in Mendrisio, Switzerland by Enrico Sassi Architetto, Davide Tommaso FerrandoStepwells of Ahmedabad, Tanvi JainRevisit: Talponia housing in Ivrea, Italy by Roberto Gabetti and Aimaro Isola, Nina BassoliOutrage: the flawed premise of the luxury bunker, Kate WagnerTunnel vision, Lili ZarzyckiUnder Jerusalem, Nadi AbusaadaIn practice: Cave Bureau, Kabage Karanja and Stella MutegiShaking the foundations, Eleanor BeaumontReputations: Cesar Manrique, Alejandro ScarpaBuilding: Soulton Long Barrow in Shropshire, United Kingdom by Sacred Stones and Greenstone Design, Phineas HarperSoulton poems with an extract from Modern Air, Merlin FulcherEditorial contributorsNadi AbusaadaToma BerlandaKhensani de KlerkMaria de Lourdes Melo Zurita