The 6G-SANDBOX project brings a complete and modular facility for the European experimentation ecosystem (inline and under the directions set by SNS JU), which is expected to support for the next decade technology and research validation processes needed in the pathway towards 6G. The target is at technologies and research advances, that span over the entire service provisioning chain, and refer to user/data, control and management planes. In this direction, 6GSANDBOX introduces the concept of Trial Networks, which refers to fully configurable, manageable and controlled end-to-end networks, composed of both digital and physical nodes. The 6G-SANDBOX Trial Networks incorporate infrastructures distributed in EU (namely in Malaga, Athens, Berlin and Oulu) and offer to third parties (including experimenters from open calls) automated experimentation capabilities through a rich and extensible toolbox. Meant to create tangible and long-term impact, the 6G KPIs and KVIs that will be quantified with the facility, will be released to any interested party; while the set of developments and APIs that will be produced, will feed an open repository as an initial step to move the contributions and the lessons learned beyond the project boarders and define a European 6G library.