Companies today have increasing amounts of data at their disposal, most of which is not used, leaving the data value unexploited. In order to leverage the data value, the data must be democratized, i.e., made available to the company employees. In this context, the use of enterprise data marketplaces, platforms for trading data within a company, are proposed. However, specifics of enterprise data marketplaces and how these can be implemented have not been investigated in literature so far. To shed light on these topics, we illustrate the characteristics of an enterprise data marketplace and highlight according marketplace requirements. We provide an enterprise data marketplace architecture, discuss how it integrates into a company's system landscape and present an enterprise data marketplace prototype. Finally, we examine organizational and technical challenges which arise when operating a marketplace in the enterprise context. In this paper, we thereby present the enterprise data marketplace as a distinct marketplace type and provide the basis for establishing it within a company.