This is the 1st UNDARK workshop, to be held in the  Instituto de Astrofísica de Canarias (IAC) during 29 September - 3 October 2025. This workshop will focus on astrophysical probes of fundamental questions related to the dark universe, with a specific emphasis on radio wave observations, as well as their possible connections with gravitational wave detection. The meeting is organized in the context of the UNDARK project and it aligns with the observational and instrumental expertise of the IAC in microwave astronomy, including experiments such as QUIJOTE, TMS, LSPE-STRIP, and GroundBIRD.