Fluids move the world, from shaping our engineered subsurface to driving the evolution of entire planets. In this talk, I present two sides of fluid dynamics across vastly different scales. First, I’ll share how we experimentally validate models of fluid flow and transport through porous media, with real-world applications in CO₂ storage and nuclear waste disposal. These models tackle the messy, multiscale challenges of predicting how fluids behave underground. Then, we’ll leave the surface behind and dive deep into high-pressure, high-temperature experiments that measure fluid viscosities under conditions found in planetary interiors. These measurements are key to unlocking how planets convect and evolve over time. Through modelling and experiments, this research addresses key questions in fluid dynamics, from subsurface engineering to planetary science.