The 2012 discovery of the Higgs boson with the Large Hadron Collider (LHC) was a groundbreaking achievement for high energy physics. Remaining puzzles such as dark matter confirm the need for beyond the Standard Model physics, and the Higgs boson can be used as a compass to determine its nature. This talk focuses on novel ATLAS searches in under-covered phase space, specifically long-lived particles and heavy resonances, that make use of the Higgs along with advanced data analysis techniques such as machine learning and anomaly detection for broad sensitivity. The High Luminosity LHC, the corresponding ATLAS detector upgrade, and studies for future colliders are all crucial for the longevity of these searches. These topics are discussed in the context of long-term planning for future experiments and the continued success of the field.