In a device (1) for rapid pressure-freezing an aqueous sample (3), such as a biological specimen, a pressurized cooling medium can be fed into a high-pressure chamber (11) into which a sample holder (30) containing a sample (3) is inserted and which is sealed with a pressure-tight seal, to the location of the sample holder (30) held therein. The high-pressure chamber (11) comprises a viewing window structure (2) with a pressure-tight window (20), through which light can be directed from the outside onto the sample (3) located in the sample holder (30). The window (20) can comprise a transparent window element made of a high-pressure-resistant material, wherein the window element (20) is held by a pressure- and temperature-resistant window bearing provided in the high-pressure chamber.