HIPPIE is a soft X-ray beamline on the 3GeV electron storage ring of the MAXIV Laboratory, equipped with a novel ambient-pressure X-ray photoelectron spectroscopy (APXPS) instrument. The endstation is dedicated to performing it in situ and it operando X-ray photoelectron spectroscopy experiments in the presence of a controlled gaseous atmosphere at pressures up to 30mbar [1mbar = 100Pa] as well as under ultra-high-vacuum conditions. The photon energy range is 250 to 2200eV in planar polarization and with photon fluxes >10$2$photonss$$-$1$ (500mA ring current) at a resolving power of greater than 10000 and up to a maximum of 32000. The endstation currently provides two sample environments: a catalysis cell and an electrochemical/liquid cell. The former allows APXPS measurements of solid samples in the presence of a gaseous atmosphere (with a mixture of up to eight gases and a vapour of a liquid) and simultaneous analysis of the inlet/outlet gas composition by online mass spectrometry. The latter is a more versatile setup primarily designed for APXPS at the solid--liquid (dip-and-pull setup) or liquid--gas (liquid microjet) interfaces under full electrochemical control, and it can also be used as an open~port for it ad it hoc-designed non-standard APXPS experiments with different sample environments. The catalysis cell can be further equipped with an IR reflection--absorption spectrometer, allowing for simultaneous APXPS and IR spectroscopy of the samples. The endstation is set up to easily accommodate further sample environments.