A hard place is another name for another rock; it is a creative way of saying there are no comfortable choices -- you go one way, you hit a rock, you go the other way you're up against a rock, you're in a bind, caught in irons, suspended on the horns of a dilemma, forced to choose between the lesser of two evils, out of leeway and sitting in a problem.

Scylla and Charibdis were colliding pillars of rock which tower up out of the sea at the north end of the Straits of Messina, between Italy and Sicily; one of them has been worn down over the centuries, and is little more than a big boulder, but the other is still dramatic. However, they do not collide with each other at regular intervals, as Homer had it. The currents are very strange at that end of the Strait, and they may have been what gave rise to the poetic legend of colliding rocks.

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