Sailors unknowingly land and camp on creature

Aspidochelone

When ships approach and crews disembark onto its back, the creature remains still, allowing them to set up camp and light fires.

Zaratan

Sailors would unwittingly land on its back, only to be plunged into the ocean when it awakens and dives.

Lyngbakr

It lies in wait, sometimes for years, until unsuspecting sailors mistake its back for a welcoming island shore.