This article describes the EGO-TRAP project in which students' visits to the Experimentarium science centre in Copenhagen, Denmark, are structured via their mobile phones. EGO-TRAP, so called because it engages visitors in a personal investigation, has been developed with the aim of creating a structured learning experience for children visiting the Experimentarium. It is designed as a virtual extension of the interactive exhibits at the centre. Although initially directed at young people from high schools in Denmark, a version for primary school children is now being developed. EGO-TRAP uses features often found in computer games and applies them to the concrete physical environment of the science centre. The mobile phone was chosen as the vehicle for creating an interactive story at the science centre because, among other things, mobile phones have the capacity to organise information.