Deepsea trenches mark where oceanic plates begin their descent into the mantle. Geoscientists want to understand oceanic trenches because they provide important constraints on the key plate tectonic process of subduction and because they let us look directly into the mantle. Especially interesting to both scientists and the public is the southern Mariana Trench because this hosts the deepest place on Earth - the Challenger Deep. Seafloor studies at such great depths requires overcoming severe technological challenges due to crushing pressure – more than 1000x atmospheric! In Nov.-Dec. 2024 we sailed aboard the research vessel T.G. Thompson to explore the inner (northern) trench slope around the Challenger Deep. We used the tethered seafloor vehicle (ROV) Jason/Medea down to its 6500m limit to study and sample exposed crust and upper mantle of what we call the Challenger Deep Forearc Segment (CDFS). CDFS is unlike other forearcs in many ways. It is subdivided into western (deeper, more young volcanics) and eastern (shallower, more mantle rocks) segments. We collected 155 samples and were surprised to find abundant young volcanic rocks along with mantle rocks, indicating strong and complex tectonic activity. We hope to return to continue studying this fascinating region.