Deep crustal processes underneath active collisional mountain belts commonly involve high-temperature metamorphism and crustal melting, which has stabilized the crust in the early days of our planet. Research into such processes has brought me to Sri Lanka, India, Australia, Greenland, Finland, Morocco and Spain. In addition, with Naturalis colleague Hanco Zwaan, I have studied the genesis of gem-quality sapphire in Sri Lanka, which is related to the ultra-high temperatures in that area during the late Precambrian.