Observations of directly imaged and transiting exoplanets and brown dwarfs reveal the wide-spread presence of condensate clouds. These clouds profoundly influence the energy transport through ultracool atmospheres and impact their pressure-temperature profiles. Yet, the structure and properties of these cloud layers remain mostly unknown and pose one of the great challenges in understanding ultracool atmospheres. I will show how HST’s and Spitzer’s stability and sensitivity allow us to address this challenge via an exciting new observational approach. With time-resolved spectroscopy and photometry – rotational phase mapping — we are exploring the longitudinal structure of clouds; with multiple epoch observations we are following the evolution of the cloud cover, opening a new window of atmospheric dynamics, and with the powerful combination of simultaneous HST and Spitzer observations we are exploring the vertical structures of the atmospheres.