Maxi-black holes - real navigation hazards

Some of the physics that would be found outside black holes, if such objects really do exist in the Universe, is described. The subject is considered in relation to teaching and matters considered include the Schwarzsch radius, density problems, and the effect of the local acceleration of gravity due to black hole chasms. The impossibility of flying through the event horizon and coming out in another Universe, as postulated by some authors, is demonstrated. (U.K.)