Superconductivity in iron-based systems can be probed using Scanning Tunneling Microscopy (STM) in a surprisingly large range of magnetic fields and temperatures. The high values of the critical field and the critical temperature, the well-defined superconducting gap, and the capability to obtain atomic resolution, often in areas free of structural surface reconstructions, provide a rare situation where STM can probe superconductivity in ranges that are inaccessible in other systems. Characteristic aspects of pnictide superconductivity are nematicity and the ubiquitous appearance of atomic scale density modulations of the superconducting gap, termed pair density waves. In this talk I will discuss vortex lattice experiments in FeSe showing how nematicity shapes the structure of the vortex lattice. Experiments at high magnetic fields provide a novel phase in which vortices coexist with a pair density wave. I will also present a magnetic field induced pair density wave in CaKFe4As4 and discuss a significant enhancement of the critical temperature of KFe2As2 recently observed with STM.