The rugged limestone hills rising sheer above the Tawe valley created an Alpine scene that sought sympathetic architecture. Here it was that Captain Powell created his neo-gothic castle. He used local limestone for the original building but the cost ran away with him and he was unable to complete the north wing. 

In 1843, the family moved in, and Captain Powell settled to the life of a country gentleman, becoming a county magistrate and a High Sheriff of Brecknock. Although both he and his father married well, misfortune began to fall upon the family when cholera took his younger son in 1851. He suffered the loss of his wife and his daughter before he died in 1862.

The estate had been entered into Chancery and was finally bought by Morgan of Abercrave for £6000.  Mr Morgan and his family settled at the castle where his son, also Morgan, joined him soon afterwards. Both families lived together happily for several years

As the decade grew toward it’s close, the current owners decided to leave, and a remarkable chapter in the history of Craig-y-nos was about to unfold. 

In 1878, the castle and its setting captivated the leading opera star of that day, who felt she had found the home of her dreams amid the calm isolation of this beautiful valley. It’s name alone strikes a romantic note and in rough translation means ‘Rock of the Night’.
This small estate in the mountains of Wales appealed to Madam Adelina Juana Maria Patti, who bought the castle and surrounding park land for £3500.

The prima donna had reached the soaring heights of a spectacular career and was to spend the rest of her life at Craig-y-nos, leaving to sing in the premier opera house of Europe and elsewhere, captivating the world with her flawless soprano voice.

She set about spending an estimated £100,000 in renovations and adding to the castle. The theatre at the mansion was a remarkable addition and could hold 150 people. It was designed as a private auditorium where an international Queen of Song could enthrayl with her remarkable voice, all those who came to listen. The opening ceremony took place on the 12th July 1891, when the list of guests included the Spanish Ambassador and Baron Julius Reuter, founder of the Foreign News Agency. 
The winter garden was another architectural feature to be built for the Baroness at the end of the 19th century. A spacious building with a soaring roof and made mainly from glass, this was where the Diva would promenade with her guests among tropical plants whilst exotic birds flew within. A pair of iron fountains fashioned as cranes with multi-coloured plumage shed rainbow light from their falling waters and captivated all who saw them.

Once again, time and the war brought change to the castle, and in 1918 the Prima Donna presented her winter garden to the people of Swansea where it became the Patti Pavilion and has been restored. One of the fountains stands in the forecourt of the castle and the other is said to exist in the grounds of Swansea University. 
 

The cost of running Craig-y-nos can be gauged from the forty tons of coal supplied each month, most of which was used for domestic heating and horticulture, fluctuating according to season.

Craig-y-nos was also the first private house to be wired for electricity.

The Diva remained at the castle during the twilight years of her life and music remained her first love. She would practice her scales daily, sometimes accompanied by her three parrots, one of which was eighty years old.

The story of Craig-y-nos changed once more with the death of Adelina Patti on the 27th September 1919, at her home in the Welsh hills. Her embalmed body lay in her private chapel until the 24th October when she was then taken to London for all the world to pay homage to her memory at the Roman Catholic Church in Kensal Green.

Since her death, stories have been told of her benign presence being seen or felt over the years. The tiny figure of a lady dressed in black is said to have been seen gliding across different rooms and drifting around the courtyard.

One recent story tells of a lady pianist who once sat at a piano in an ante-room of the theatre and then felt a presence behind her. At her first attempt she played the whole of Patti’s ‘Home sweet Home’ perfectly, before turning round to find no one there.

The castle and the grounds were sold to the Welsh National Memorial Trust for £11,000 in March 1921, and it was called the ‘Adelina Patti’ Hospital at the request of the Baron. It functioned as a chest hospital and many were nursed back to health during this period until the scourge of tuberculosis was conquered. In its latter years, the patients were mainly elderly and infirm.


During the Second World War an RAF pilot was brought to the hospital for treatment and met a young woman who was almost confined to her bed. They decided to wed but she was too ill to travel so the church granted them a special dispensation. They were married in the theatre and returned to the outside world after recovering their health. 

The castle finally closed as a hospital on the 31st March 1986 after the transfer of remaining patients to the new Community Hospital at Ystradgynlais. The Welsh Office maintained Craig-y-nos Castle and its unique theatre until it was sold into private ownership.

ref : http://www.craigynoscastle.co.uk/latest-news/Castle-History-Craig-Y-Nos-Castle/