Miquel Ardid Ramírez, Universidad Politecnica de Valencia/ANTARES/KM3NeT We describe the technological and scientific challenges of the undersea neutrino telescope ANTARES and KM3NeT. ANTARES is a neutrino telescope located in the Mediterranean Sea with the aim of detecting high energy neutrinos of extra-terrestrial origin. It is the largest one in the Northern hemisphere and consists of a 3D array of 885 photomultiplier tubes arranged in 12 detection lines, able to detect the Cherenkov light induced by upgoing relativistic muons produced in the interaction of neutrinos with the surrounding water and seabed. The scientific scope of neutrino telescopes is wide, being their most relevant goals the search for neutrino astrophysical sources and the indirect detection of dark matter particles. The current status of this telescope and the first results are shown. Moreover, the deep-sea research infrastructure to be constructed in the Mediterranean Sea, KM3NeT, hosting a neutrino telescope with a volume of at least one cubic kilometer will be presented as well. Finally, we will focus on the acoustic activities in these infrastructures, in which our research group is involved. Acoustic systems are used to monitor the positions of the optical detection modules whose positions vary with time as an effect of undersea currents, and may be used for studies towards acoustic detection of ultra-high energy neutrinos.