A castle built for show became a gift to strangers
A private fantasy on the cove ended up belonging to everyone who visits it.
Last reviewed 19 September 2026 · A four-minute read · 2870 BC–2000
The short answer
The Forte de Nossa Senhora da Luz de Cascais, better known as the Torre de São Sebastião, is a Neo-Gothic and Moorish-style tower built in 1900 for the aristocrat Jorge O'Neill on a cove at Cascais. Later owned by the Count of Castro Guimarães, it became a public museum in 1931 and still holds his manuscripts and art.
Marina, Cascais, Portugal — 2008 · Pedro Ribeiro Simões from Lisboa, Portugal · CC BY 2.0
1900
O'Neill built a fantasy castle on a cove
Jorge O'Neill built himself a castle. He called it the Torre de São Sebastião, and he meant it to look like something out of the Middle Ages.
O'Neill was a Portuguese aristocrat with a distant Irish name and a very modern fortune. He held Portugal's match monopoly business. This was one of several ventures that made him rich. He had enough money to build whatever he wanted on this stretch of coast at Cascais.
What he wanted was strange and specific. The architect Francisco Vilaça mixed Neo-Gothic arches with Moorish horseshoe windows. O'Neill filled one room with shamrocks. This was a nod to Irish blood four generations back. The house juts a stone tower out over a small cove, thirty paces from where the water breaks against the rock.
Inside, the rooms run into each other under beamed ceilings and tiled stoves, some of them stripped out of other buildings entirely and rebuilt here. It was a rich man's fantasy of a castle, built by a man who had never needed to defend one.
O'Neill did not stay long. Ten years after he finished it, he sold the house.
The next owner filled it with something older than the building itself.
1910 to 1927
A count filled the castle with rare manuscripts
In 1910, the 1st Count of Castro Guimarães bought O'Neill's castle and moved in with his wife.
He spent the next seventeen years turning the house into a private treasury. He commissioned a neo-Gothic organ built just for the building. He tracked down rare sixteenth-century manuscripts. One was a copy of the Chronicle of Don Afonso Henriques. This was the account of Portugal's first king. Duarte Galvão wrote it in the fifteen-hundreds.
The Count died in 1927. He left instructions before he went: the house and its garden were to pass to the state, on one condition. It had to become a museum, open to anyone who wanted to walk through it.
The Condes de Castro Guimarães Library Museum opened its doors on July 12, 1931. For years it was the only museum in Cascais. A castle built by one man to impress his friends became the property of everyone who walked in off the street. It still has that status today.
A castle built to look medieval ended up holding an actual medieval chronicle.
1877 to 1882
A king's tide gauge began recording nearby
Before Castro Guimarães filled his castle with manuscripts, a different obsession was already running along this same shore.
King Carlos I loved the sea. He was a trained oceanographer. He ran twelve of his own scientific expeditions off this coast. In 1882, he had a sea-level recorder installed near his marine biology lab. It went in the Citadel of Cascais. The citadel had guarded the town since 1488. The instrument itself was built earlier, in 1877, by clockmakers in Paris.
It measured the tide with a float, a system of pulleys and a pen that scratched a line onto rotating paper. Portugal's mapmakers used its readings to fix mean sea level for the entire country's surveys.
The gauge moved about a hundred feet from its first spot before the century was out, chasing more reliable water. It has run without stopping since 1895. It still records the sea rising, about 15 centimeters higher now than when a king first switched it on.
Not every private venture on this cove ended so well.
1606
A spice ship sank off this coast
Long before any of these houses stood, the sea off Cascais took a fortune down with it.
The Nossa Senhora dos Mártires shipwreck was a Portuguese merchant ship coming home loaded with pepper and spice. In 1606, rough weather caught her near the mouth of the Tagus, close to this stretch of coast, and she went down.
Divers later gave her a nickname, the Pepper Wreck, for the cargo still packed in her hold. She sank at the tail end of Portugal's age of empire. Ships like hers were the difference between a fortune made and a fortune lost at sea.
The wealth that later built castles on this cove first had to survive the water in front of it.
1890 to 1902
A secretary built his own private fantasy nearby
A short distance from O'Neill's tower, another rich man built his own private fantasy at the same time.
Bernardo Pinheiro Correia de Melo was private secretary to King Carlos. He designed a summer house he called Casa de São Bernardo in 1890. It took twelve years to finish. He built it to resemble the farmhouses of Minho, the province in northern Portugal where he was born.
The house became a dinner table for a group of writers who called themselves the Vencidos da Vida, the Life's Vanquished. The novelist Eça de Queirós was a regular guest and often stayed the night. King Carlos himself sometimes joined them, and would sit and paint watercolors in the house.
Correia de Melo's family did not keep it. The house passed out of private hands. It now belongs to the Cascais Marina. The Marina is a working stretch of water two hundred feet from the tower O'Neill built to look like a castle.
The cove still holds three private fantasies, and none of them belong to a private person anymore.
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Prehistoric
2870-2475 BC
Radiocarbon samples pulled from ground about 900 meters away date to between 3008 and 2475 BC, evidence people were working this coastline long before Cascais existed.
The town around you was chartered as its own municipality in 1364, a status it held for nearly five centuries before Portugal reorganized its local government.
The Church of Nossa Senhora da Assunção, the town's mother church a few streets away, has interior decoration dated to 1520-1525 and appears in a 1572 engraving of Cascais seen from the sea.
Somewhere between 1575 and 1625 another Portuguese ship returning from India sank in the bay, and archaeologists found its wreck in 2018 loaded with pepper, Chinese porcelain, bronze cannon and cowry shells used in the slave trade.
Parts of the Cascais Cultural Centre, close to the citadel, date back to the end of the 16th century when the building was a Carmelite monastery, before it reopened as a cultural center in May 2000.
In 1606 the merchant ship Nossa Senhora dos Mártires sank in a storm at the mouth of the Tagus carrying pepper and spice, wreckage now known to archaeologists as the Pepper Wreck.
Just off the marina, the Cascais tide gauge began recording sea levels in 1882, the first such instrument in Portugal and still in use, giving Portugal its reference height for elevation.
Casa de São Bernardo, a short walk from here, was designed in 1890 for Bernardo Pinheiro Correia de Melo, First Count of Arnoso and private secretary to King Carlos, but the building was not finished until 1902.
In the late 19th century the aristocrat Jorge O'Neil bought land nearby and had architect Raul Lino design Casa de Santa Maria, now a historic house museum and a landmark of Portuguese Summer architecture.
The Palácio dos Condes de Castro Guimarães, originally called the Torre de São Sebastião, was built in 1900 as an aristocrat's summer residence and became a museum in 1931, its rooms now holding paintings and porcelain of national significance.
The Cascais Marina in front of you, now the largest on the Portuguese Riviera and the third largest in the country, opened on August 6, 1999, and later hosted America's Cup events.
Before it became a museum in 1931, the building was a private summer residence called the Torre de São Sebastião, built in 1900 for the aristocrat Jorge O'Neill and later filled with manuscripts and art by the Count of Castro Guimarães.
Who built the Torre de São Sebastião?
Jorge O'Neill, a Portuguese aristocrat who held Portugal's match monopoly, commissioned the tower in 1900, working with architect Francisco Vilaça to mix Neo-Gothic arches with Moorish horseshoe windows.
Why did the castle become a museum?
The Count of Castro Guimarães, who bought the house in 1910 and filled it with manuscripts and a purpose-built organ, left instructions on his death in 1927 that the house and garden pass to the state on condition it become a museum open to the public.
What happened at Cascais in 1606?
In 1606 the merchant ship Nossa Senhora dos Mártires sank in a storm at the mouth of the Tagus near Cascais while carrying pepper and spice; divers later nicknamed the wreck the Pepper Wreck.
What is the connection between this castle and King Carlos I?
King Carlos I, a trained oceanographer, ran scientific expeditions off this coast and in 1882 had a sea-level recorder installed at the Citadel of Cascais nearby, around the same period the castle and neighbouring houses were being built.
