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Non-conventional core-guided transmission windows within the visible spectral range are identified in commercial hollow-core photonic crystal fibers designed to operate at 1550 nm. These windows are likely to be related to higher-order cladding photonic bandgaps and are found to be highly dependent on the cladding microstructure, thus being affected by pressure-induced stress/deformation. 20-cm-long fiber samples are then used to demonstrate simple and temperature-independent hydrostatic pressure sensing with two different setups. While in the first setup pressure is externally applied to the fiber and results in operation in the hundreds of kgf/cm 2 (or tens of MPa) range, the second setup applies pressure directly to fiber internal microstructure and is sensitive to pressures down to a fraction of kgf/cm 2 (hundredths of MPa). The fact that pressure is directly transduced into transmitted power greatly simplifies the required sensor interrogation setup.