The retreat of sea ice in the Arctic is one of the most obvious indicators for ongoing changes in our climate system. Sea ice extent is monitored from satellites over the last decades and reveals an important time series. But this retreat is directly related to many other phenomena as the transition to a younger, thinner, and more seasonal ice cover. It has strong impacts on various components of the climate and ecosystem. But many processes and interactions are less obvious than the transition from a white, ice covered to a more blue ocean. Here I present different aspects of how we, the sea ice physics group at the Alfred-Wegener-Institut, observe the physical properties of Arctic sea ice. I will give an overview of the applied, partly new and innovative, methods to observe the mass- and energy budget of sea ice on different time and length scales. Beyond this, highlights of recent studies are summarized. Airborne measurements of sea ice thickness reveal how sea ice volume has decreased over the last years. These measurements are also used for comparisons to sea ice thickness measurements from the CryoSat-2 satellite. An other focus of our work is the quantification of the interaction of sunlight and sea ice. Radiation measurements over and under sea ice reveal changes in the optical properties of sea ice and their implications for the energy and mass budget. In addition to measurements during expeditions with the icebreaker Polarstern, autonomous platforms (buoys) add to our data sets. Finally, the combination of local, autonomous, and regional measurements with additional large-scale observations allows us to discuss key processes over large regions and during different seasons.