Plaža Betina špilja

This guide to Plaza Betina spilja, a sea cave near Dubrovnik, follows Marin Getaldic, a nobleman-turned-mathematician who around 1600 hand-ground a parabolic mirror barely two feet wide and brought it here to test on driftwood and cloth. You'll hear how word of his fire-starting experiments reached Padua, sparking a correspondence with a young Galileo Galilei, and drew later citations from Christiaan Huygens and Edmond Halley. Stand in the cool cave and notice the still water and walls that once kept the wind off his flame.