We’ve built them up all over the world and they’re impressive—bustling metropolises packed with millions of people moving about in orderly chaos. Concrete Jungle is Hamburg-based photographer Kai-Uwe Gundlach‘s vibrant look at mega-cities in China, Spain and the U.S., shot while he was traveling in 2008 and 2009. Captured in painterly palettes of color, Gundlach’s geometric urban hubs link a city’s massive growth with nature’s forced retreat, asking us to contemplate the balance between a fascinating yet frightening global reality.