The ATLANTIS test center is a proving ground for marine robots and related technological solutions, geared towards Offshore Operations and Maintenance (O&M). Installed in Viana do Castelo, the ATLANTIS Test Centre is composed of two test sites, the Coastal Testbed, and the Offshore Testbed, as well as a Shore Control Centre. The Test Centre is uniquely located, capturing the unique conditions of the Atlantic Ocean, while also providing a more sheltered and controlled environment for testing robotic technologies, which allows it to cover the testing of technologies covering the full range of TRLs. The Coastal Testbed is located within the harbor of Viana do Castelo, and presents a controlled, near-real environment. It is composed by a decommissioned floating offshore structure, that replicates the challenges presented in floating offshore wind farms. Due to its more protected environment, the Coastal Testbed is geared towards the testing of less mature technologies, with a lower TRL, allowing not only its validation, but also the de-risking of robotic technologies and new methodologies for offshore O&M. The Offshore Testbed is composed of a real wind farm, the WindFloat Atlantic Wind park, located up to 20 kilometers from the coast of Viana do Castelo. It consists of three floating wind turbines, with access through a support vessel at the disposal of the Test Centre users. As it is a real offshore wind farm, the Offshore testbed is geared towards the demonstration of mature technologies, with higher TRLs, and closer to market. The Shore Control Centre (SCC) allows the planning and monitoring of all operations taking place in the ATLANTIS Test Centre. It provides full communication with the robotic platforms on both testbeds, in addition to having direct line of sight communication with the vehicles operating in the Coastal testbed.