On the other side of the strait was Scylla, another sea-monster. The two sides of the strait are within an arrow's range of each other, so close that sailors attempting to avoid Charybdis will pass too close to Scylla and vice versa.
The Argonauts were able to avoid both dangers because they were guided by Thetis, one of the Nereids. Odysseus was not so fortunate; he chose to risk Scylla at the cost of some of his crew rather than lose the whole ship to Charybdis.
Traditionally this has been associated with the Strait of Messina between Italy and Sicily. Despite being more than two miles wide at its narrowest point, not to mention three and a half miles wide at the rock traditionally identified as the home of Scylla, whilst the minor whirlpools traditionally identified as Charybdis are not even in the narrows, this identification has stuck. Recently scholars have looked again at the location and suggested this association was an erroneous later identification and that a more likely origin for the story could be found near Cape Skilla in north west Greece.