Watching an episode of the Cleaner and they refer to a sea monster called the Oilliphéist

Apparently

“an Oilliphéist cuts the route of the River Shannon when it hears that Saint Patrick has come to drive out it and its kind.

In a comic addition to the story, the monster swallows a drunken piper named Ó Ruairc (O’Rourke). The piper is either unaware of his predicament or is completely unperturbed and continues to play inside the Oilliphéist’s stomach. The monster becomes so annoyed with Ó Ruairc’s music that it coughs him up and spits him out.” The Olliphéist - Wikipedia

A sea monster - not necessarily an Olliphéist, sadly