In this paper we describe the practical implications of semantically exposing a collection management system (EROS [1][2][3][4]) for large cultural heritage multimedia repositories. This is achieved through a Search and Retrieve Web Service (SRW[5]) that maps the EROS metadata schema to the CIDOC Conceptual Reference Model[6], a core ontology for describing the semantics of schema and data structure elements in cultural heritage documentation. The mSpace([18]) framework, an interaction model to help people access and explore information, has been integrated with the SRW to provide powerful navigation facilities on the rich multimedia collections served by EROS. We also present some of the lessons learnt whilst adapting the technologies to the EROS system and offer some insight into the performance issues with a system of this size.