ECHO is an immersive, site-specific, audiovisual collaboration between a visual artist and a composer, which was developed especially for the St. Andrew’s Church in Hildesheim. ECHO explores the acoustic and architectural qualities of the church through a synergetic experience of sound and light. The reverberation in the main hall of the church is enormous and very intense; there is a natural delay of several seconds. The electroacoustic composer Augusto Meijer uses these spatial qualities in a soundscape based on digitally modified samples of the church’s famous organ. His sounds wander and push through the main hall, where they overlap, reinforce or attenuate each other. Jaap van den Elzen uses these properties in his light landscape to create a dialogue, a (dis)harmony between sound and light. Narrow beams of apparently massive light, moving in both horizontal and vertical directions, reflect through the space. They trace the architectural structure of the church to explore and reveal its beautiful spatial qualities in various patterns. From total chaos to hyper-structuring, the installation creates a distorted perception of space and time to become an immersive, multi-sensory environment in which visitors can linger.