You can have an out and back route. You can also have events that have a figure of 8, although I believe the Faccombe 100 was frowned upon because it consisted of elaborate twists and turns to keep it in an audaciously hilly part of the Wiltshire-Berkshire-Hampshire border (2250m ascent in 100km of southern softy territory) meant it never went more than about 12km from the start/finish point.
My memory is a little hazy, but I don't think the Faccombe event repeated much at all (in the same direction). Though it was indeed frowned upon, for two reasons. There was always a bit of a question mark over the actual amount of climbing / stupidity points awarded, though I never understood why as a contour count is not terribly onerous on a 100. And the event had a ridiculous number of info controls / checkpoints to preserve route integrity. That was my first audax, back in 2000