Cestyll gardens and house were bought by the Hon. Walter Vivian for his niece Violet in 1918. On their deaths their ashes were scattered in the garden at Cestyll. When the land was sold by the family to the C.E.G.B. as part of the power station grounds they included in memorium, a covernant,stating that the company should maintain the garden in perpetuity.

"Violet Vivian was the maid of honour to Queen Alexandra," said Eirlys Mason of the Wylfa information team. "She and her twin sister Dorothy were very popular at Court and friendly with Princess Victoria, the daughter of Edward VII.

Victoria was also very interested in gardens and helped design the lower part of the garden at Cestyll. There was a pane of glass in the window of Cestyll house, inscribed with a diamond ring by Princess Victoria, with the words, "Thanks for good times spent at Cestyll". The glass was removed prior to the sale by the owner Lady Astor of Hever, niece to Violet Vivian.

The site is a collection of rock gardens, shrubs and trees with the River Cafnan running through the centre.

"It really is a secret garden," said Eirlys, who's worked at Wylfa for many years. "You have to come through two farmers' fields to get access to it and they're only open to the public by request, or if charities ask to open them to raise funds.

"For many years the RNLI have opened them each May bank holiday, but other charities are welcome to apply to open them in August."

The gardens, which are registered with CADW for their historical importance, are unique as few from the 1920s have survived in such an unspoilt way.

"They've used the natural flow of the river Cafnan and landscaped round it", said Eirlys. "It took about 12 gardeners to create it with Violet, though she had a lot of help in deciding which plants to use because of her Royal connections with the National Botanical Gardens in Kew.

"They helped her select plants which could be adapted for this coastal area, though they planted the belt of pines later to give shelter from the wind."

Tons of soil was brought into the garden by hand in the 1920s, to enable shrubs to grow on the rocky terrain. The east-facing escarpment used to be covered in top soil and planted with over 3,000 bedding plants each year.

There's a 19th century mill in the gardens, now owned by the National Trust - though it can only be visited by prior arrangement.

A mill has stood on the site since the 13th century and this one is unusual in that the wheel is driven by water flowing over it, rather than underneath.

There's also a pump house which was used to supply the house and gardens with water - but turned out to be a lifeline for Wylfa.

"The station managed to pump water from the river during a strike by the water board," said Eirlys. "They set up a series of pumps to fill the million gallon water feed tank at Wylfa; so the gardens saved the station in a way."

For further information on how to visit the gardens, please contact Wylfa Power Station visitor centre.