In this article, we discuss how quantum physics and relativity can be taught in upper secondary school, in ways that promote conceptual understanding and philosophical reflections. We present the ReleQuant project, in which web-based teaching modules have been developed. The modules address competence aims in the Norwegian national curriculum for physics (final year of upper secondary education), which is unique in that it includes general relativity, entangled photons and the epistemological consequences of modern physics. These topics, with their high demands on students' understanding of abstract and counter-intuitive concepts and principles, are challenging for teachers to teach and for students to learn. However, they also provide opportunities to present modern physics in innovative ways that students may find motivating and relevant both in terms of modern technological applications and in terms of contributions to students' intellectual development. Beginning with these challenges and opportunities, we briefly present previous research and theoretical perspectives with relevance to student learning and motivation in modern physics. Based on this, we outline the ReleQuant teaching approach, where students use written and oral language and a collaborative exploration of animations and simulations as part of their learning process. Finally, we present some of the first experiences from classroom tests of the quantum physics modules.