In his poem "Inchcape Rock," Robert Southey does not describe the rock itself at any great length. He notes simply that it is "perilous," but the story of the poem makes it clear why this is.
The "Inchcape Bell" has been put on the rock so that sailors will hear it ringing and therefore know that they are coming close to the rock. Without the bell, it is very difficult to see the rock in time to be aware of its presence and to avoid it. In this poem, Southey describes how Sir Ralph has his men cut down the bell so that other sailors will run aground on the rock. However, when he later returns after many years with the "plunder" from his piracy, he forgets that he cut down the Inchcape Bell himself. Expecting to hear it, he does not notice Inchcape Rock until it is too late, and his ship has run aground on it. He has reaped the rewards of his own villainous behavior.
In reality, Inchcape Rock is often also called Bell Rock because of its association with the story of the Inchcape Bell. It is off the east coast of Scotland near Dundee, and today its lighthouse serves the same function the Inchcape Bell once was supposed to.