The multiplication of real-time data sources in urban areas creates a fragmented environment regarding the supply of mobile services for transportation. Thus, in order to support the deployment of smart mobility services with a more global view of the urban context, the available data must be appropriately handled through dedicated platforms. It is in this context that the Connecting Digital Cities (CDC) project has been initiated at European level. The goal of the project is to deploy a platform that is able to collect, analyze and enrich the relevant information in order to provide a valuable aggregate of real-time data related to urban mobility. This paper presents a first return of experience in the development of this platform. We first provide an overview of the CDC project and we detail the architecture of the platform intended to collect and process real-time data. For validation purposes, we then describe a mobile service for multimodal journey planning that has been deployed to interact with the CDC platform. Finally, we share the lessons learned in terms of reliability of the system and proper integration of the system into urban ecosystems.