She was the scourge of Spanish and English merchants. "Notorious by land and sea," her English enemies said. Queen Elizabeth I even put a price — 500 pounds — on her head.

Grace O'Malley, a 16th century pirate, was feared from Ireland's Galway Bay to Hampton Court in England. A clan chieftain and a sea captain, she once commanded 200 men and a flotilla of galleys and held sway in the west of Ireland in an era when most women led constricted lives.

Little about Grace is written in Irish history, but she is celebrated in legends, ballads and songs, and four centuries after her death there's a growing interest in her exploits.

I first encountered the stories about the free-spirited pirate queen, nicknamed Granuaile, while researching a book about seafaring women in the North Atlantic. Last May, I returned to Clew Bay for a week to do more research and revisit the castles from which Grace ruled and raided.

I traveled west by train from Dublin to Westport, a convenient base from which to explore. The four-hour train trip, which passes through some of the greenest pastures in Ireland, gave me a chance to reread Anne Chambers' biography "Granuaile: Ireland's Pirate Queen, c. 1530-1603" (Wolfhound, 2003). Chambers' book sets her life against the tumultuous 16th century, when English colonization of Ireland became too powerful to resist.

Grace was born in 1530 to Margaret and Dubdhara "Black Oak" O'Malley, the leader of a seafaring clan. Her father recognized that young Grace had an eye for the weather and aptitude for the sailor's life. There's a story that she cut off her hair to look more like a boy and better fit in on board. Another says she flung herself down from the mast onto the back of an Algerian pirate about to attack her father. Whether the tales are true, they suggest that Grace's rebellious, brave character was apparent early on.

Those traits served her well in the tempestuous Ireland that she was born into. The country was fragmented into warring fiefdoms, each controlled by a clan. Raiding and cattle stealing were the norm. Paradoxically, it was the disorder of the 16th century that allowed Grace to mature from a wild girl into an enterprising and canny woman who played both sides, winning a meeting with Queen Elizabeth and a peerage for her son, yet remaining an Irish heroine.

Westport, an attractive Georgian town on the shores of Clew Bay, is centered in O'Malley territory, and I stayed a night in Westport at the Olde Railway Hotel, whose front-facing rooms have a view of the pretty river, Carrowbeg, that runs through town. The lounge, stuffed with horsehair sofas and wing chairs, birdcages, fern stands, tables, pianos and footstools, looks barely changed from 1842, when author William Makepeace Thackeray stayed here.

The next day I set off for what is probably the only museum in the world dedicated to a seafaring woman. The Granuaile Visitor Centre is about 20 miles from Westport, in Louisburgh. Buses run there regularly, but I took a taxi. The journey took me past Murrisk, which has a ruined abbey, where Grace is said to have been baptized and then married at age 15 to her first husband, Donal O'Flaherty, a violent-tempered man who was killed in a feud with another clan.

The small museum in Louisburgh, housed in an old Anglican church, tells the story of Grace's childhood on Clew Bay, as well as her remarkable metamorphosis from a widow with three children and no land or income into the pirate queen.

After Donal's death, she returned to Clew Bay to trade with southern Europe, and occasionally and apparently with great relish, raid the merchant ships coming from Spain and Portugal to Galway. The museum has some terrific dioramas and models, including one of Grace in doublet and hose, with a sword hanging from her belt. No one knows exactly what she looked like, but clearly she had no trouble finding admirers, even when she was wearing men's clothing.

A hearty gambler

Grace O'MALLEY's pirate headquarters was on Clare Island, outermost and largest of the hundreds of isles of Clew Bay. You can take a passenger ferry to it from Roonagh Pier, a few miles from Louisburgh. The half-hour passage, often a bit rough, gives a fantastic view of the stone tower above Clare Island's harbor. Grace and her followers lived in the castle, though the Granuaile Visitor Centre suggests there would have been outbuildings all around, including a feasting hall.

Grace was known as a gambler, with cards as well as love and piracy. One story recounts how she saved a young man from a shipwreck and made him her lover. He was murdered by her enemies, and she took revenge, killing those responsible for his death and taking their castle.

Clare Island is an excellent place to walk, cycle and bird-watch. One walk runs along the coastline to a 15th century church where Grace is reputedly buried.

I stayed at an island B&B that didn't have much to offer but a room with a bed and no chairs, and irritating proximity to the family's melodious cellphones. After hiking all afternoon, I spent some of the rainy evening at the pub attached to the island's one hotel, the Bay View. Islanders were celebrating the launch of a new boat with some spirited set dancing.

The next morning, by the harbor, while I was waiting for the ferry, I took refuge from the rain in the lounge of Granuaile House, with its cozy fireplace and smells of scones and bacon, and found myself wishing I had stayed there. The owner, Bernard McCabe, offered me a cup of tea and a seat by the fire.

Back in Westport, I checked into the Clew Bay Hotel, a family-run establishment with good-sized rooms, some right over the river, and a friendly staff.

Fifteen miles north of Westport on the shores of Clew Bay stands another castle that once belonged to Grace, Carrighowley Castle at Rockfleet. The stone tower, several stories tall, is in good condition, and can be visited. Grace married her second husband, Richard Bourke, another clan leader, often called Richard-in-Iron for his habit of wearing a suit of armor.

Grace coveted his castle, Carrighowley, for its location on the innermost shores of Clew Bay, safe from the English. Legend has it that a year after their marriage and after the castle was safely in her possession, she met him at the door and said, "Richard Bourke, I dismiss you." But they remained allies after their divorce, and she bore his son, Tibbot, at sea. The story goes that a day after she'd given birth, her galley was attacked by Algerian pirates, and her men called to her for help.