This paper highlights 6G testbed requirements essential to validate new radio access for diverse services, novel functionalities and enhanced coverage. The testbed approach presented includes an architecture with four functional levels, extensive data collection, storage and processing capabilities, scalable mechanisms for transmitter calibration and synchronization, and innovative hardware such as intelligent surfaces. Open standards are proposed to facilitate widespread adoption. The paper contrasts the proposed testbed approach with notable current 6G testbed plans and implementations to compare scope and capabilities. Finally, a discussion on future directions focuses on considerations for commercially available off-the-shelf equipment, highly scalable platforms, network-of-networks validation, and capabilities that support millimeter-wave and sub-terahertz bands.