A technique is described for the indirect visualisation of magnetic domain structures through the coupling of stray surface magnetic fields into a bismuth-substituted garnet layer. The resulting magnetisation distribution within the garnet layer is visualised optically using the polar Kerr effect. A small single-crystal platelet of barium hexaferrite is used to demonstrate the method and the complex, field-induced magnetisation patterns in the garnet are discussed qualitatively. The effect of a small bias field on the magnetisation structures is also considered and has been shown to be a means of simplifying the complex images which are produced. This indirect magneto-optical method of visualising magnetic domains is both effective and convenient, although the ultimate limits of resolution for the technique remain to be determined.