In this paper, spatially resolved photoluminescence (PL) spectroscopy with various excitation wavelengths is presented as a nondestructive and versatile technique providing access to the individual subcells of multijunction solar cells. This method is demonstrated on a state-of-the-art monolithic tandem solar cell composed of a planar perovskite solar cell and a silicon heterojunction solar cell. It is shown that the lateral distribution of inhomogeneities can be attributed unambiguously to the individual cells and be related to the manufacturing process. The approach of depth-selective probing of the silicon bottom cell is verified by comparison to reflection maps and by comparison to measurements of the silicon cell after removing the perovskite top cell. Analyzing subcells integrated into a monolithic tandem solar cell is challenging though crucial in order to identify performance limiting loss mechanisms. This method can be used to improve the study of the mutual influence of adjacent subcells in the fully fabricated device, which has been an unfeasible task up to now.