Carlos J. Vargas, Caroline Kilbourne, Haeun Chung, Erika Hamden, Ralph Kraft, Joseph N. Burchett, Lauren Corlies, Claude-André Faucher-Giguère, Kevin France, Keri Hoadley, Briana Indahl, Dong-Woo Kim, Varsha Kulkarni, Jiangtao Li, Nicole Melso, Drew Miles, Nikole M. Nielsen, Anna Ogorzalek, Ben Oppenheimer, Frits Paerels, Daniel Patnaude, Molly Peeples, Frederick S. Porter, David Schiminovich, Malgorzata Sobolewska, Ming Sun, Todd Tripp, Jason Tumlinson, Sarah Tuttle, Jessica Werk, Ka-Wah Wong, John ZuHone

The circumgalactic medium (CGM) -- the multiphase gas reservoirs surrounding galaxies -- remains the least understood component of the baryon cycle governing galaxy growth, despite its central role in the Astro2020 Decadal Survey's priorities. Existing constraints come almost exclusively from pencil-beam absorption spectroscopy, leaving the spatial structure, kinematics, and phase interactions of CGM gas fundamentally unmapped. We present Ardua, a mission concept for NASA's ASTRA Initiative that combines wide-field far-ultraviolet spectroscopy with a Line Emission Mapper (LEM)-derived X-ray microcalorimeter instrument to obtain the first comprehensive emission maps spanning the full CGM temperature range, including cool neutral gas, ionized warm-hot phase gas, and the volume-filling hot corona. By observing more than 50 nearby galaxies comprehensively in the UV and X-ray, Ardua will test competing galaxy formation models, resolve multiphase gas flows and feedback-driven outflows, and extend baryon-cycle science to the intergalactic medium and the environments of exoplanet-hosting stars. Beyond its core CGM/IGM program, Ardua's wide-field, high-sensitivity instruments are designed to serve as a flexible community resource, supporting guest-investigator science across astrophysics. No planned or approved mission is designed to deliver this combined UV/X-ray survey capability.