A small area of sky in the constellation Sagittarius that is relatively free from obscuring dust, and through which an optical telescope can see to the central region of our Galaxy and beyond. The window is at galactic longitude 0°.9 and latitude −3°.9, near the globular cluster NGC 6522. W. Baade used this window to observe RR Lyrae variable stars in the central bulge of our Galaxy and to determine their distance and hence the size of our Galaxy.