Gaia is a perfect halo explorer. It makes up for a relatively shallow depth with an array of features not available to other surveys/telescopes. These include stable photometry, impeccable star/galaxy separation and resilience to artefacts, not to forget the temporal sampling. In this talk, amongst other things, I will show that in terms of detection of low surface-brightness sub-structure in the halo of the Milky Way, Gaia DR1 has capabilities that are comparable to the of large sky surveys that reach 2-3 magnitudes deeper. Moreover, by using the Gaia DR1 data to recalibrate the SDSS astrometry, we have now built an unprecedented proper motion catalogue with the quality similar to that expected for the Gaia's DR2.