Since the construction of modern facilities such as VLTI and CHARA, interferometry has become a key technique to probe massive stars and their often-complex circumstellar environments. In this seminar, I will briefly introduce the basics of this technique and its application to astrophysics. We will then start our journey around massive stars at the highest-possible angular resolution. I will show how interferometry can address various questions about massive stars through the characterisation of the geometry and kinematics of their stellar surface or environment. We'll talk about stellar formation, binarity, mass-loss, and rotation. Finally, we'll see how the latest generation of instruments which combine the power of interferometry and spectroscopy offers amazing spectro-imaging capabilities.