To the uninitiated visitor, Mussenden Temple is something of an enigma.
It presents many mysteries: Is it really a temple? Who built it and why? What could possibly be inside it?
A new book, The Earl Bishop by lecturer and broadcaster Stephen Price, sheds light on the fascinating story of the man behind the temple.
The Earl Bishop was in fact Frederick Augustus Hervey, fourth Earl of Bristol and Church of Ireland Bishop of Derry.
Born into a distinguished Suffolk family in 1730, Frederick Augustus was many things; scientist, agitator, art collector and Royal Chaplain to George III, who referred to him as "that wicked prelate".
In 1766 the eldest Hervey brother was appointed Lord Lieutenant of Ireland and he soon made Frederick Augustus the Bishop of Cloyne and then Bishop of Derry.
The position brought with it a very generous salary. By his late thirties, Frederick Augustus had also inherited the estates of his two brothers and was sitting on quite a fortune.
While the value of money is hard to measure over time, Stephen likens Hervey's wealth to the level of someone like Richard Branson.
"The Earl-Bishop's annual income was twice what it cost George III to buy Buckingham Palace," he said.
Frederick Augustus started to put that fortune to good use. He was a philanthropist, bestowing his charity on the people of Derry. He built roads and became actively engaged in life in Ireland.
One of his most lasting achievements was to put the Giant's Causeway on the map, both scientifically and as a tourist destination.
"Hervey was interested in vulcanology, so when he's made Bishop of Derry he immediately gravitates towards the Giant's Causeway," Stephen explained.
"We now think of the Giant's Causeway as a big tourist attraction, but back then it really was the middle of nowhere. People vaguely knew about it, but nobody really went there.
"Hervey was actually made a fellow of the Royal Society because of his work there. He established that the whole of that coastline was volcanic."
Spending so much time around the causeway was difficult for a bishop whose diocese was in Derry. If you wanted to travel from Derry to the North Coast at that time it was a good day's journey.
So, the Earl Bishop built his own holiday home at Downhill.
"The reason he chose Downhill was because that was church land and he had worked out a clever technique where he could make church land belong to him," Stephen explained.
"So it starts off as a holiday home and it grows and grows. He also starts making all these continental journeys buying art and artefacts and sending them back to Downhill. And the more art he buys, the bigger Downhill has to get to accommodate it."
At its peak in the 1790s, Downhill contained Rembrandts, Rafaels, Titians, Durers, Carravagios, artistic names that today would not be seen outside a major gallery.
The Earl Bishop had a particular attraction to the art scene in Italy.
"The art community in Rome used to love to see him coming because when he turned up it really was bonanza time," Stephen said.
It was in Rome that Hervey fell in love with a Roman temple dedicated to the goddess Vesta.
"Hervey wanted to buy the temple and bring it back to Ireland and re-erect it," Stephen explained.
"But the Pope refused his offer. So he gets his architect to sketch the temple and he builds his own copy at the edge of the cliff at Downhill."
The building was dedicated to the Earl Bishop's cousin Frideswide Mussenden - hence Mussenden Temple.
Once built, it was used by Hervey as a cliff-top library and was ornately decorated inside.
Underneath the building, Hervey built a room for Catholic priests to say Mass, a provocative decision during the time of the anti-Catholic penal laws.
Although a bishop in the Church of Ireland, Hervey was a powerful proponent of religious equality and dedicated himself to improving the lot of Catholics and Presbyterians in 18th Century Ireland.
He financially supported, not only his own church, but those of his Catholic and Presbyterian neighbours.
"He saw that Ireland would never be a peaceful place until religious discrimination was effectively ended," Stephen said.
"There are things that he said in the 1780s and you read them now and you think 'my god, there's the next 200 years of Irish history'."
However, Stephen thinks the Sisyphean task the Earl Bishop had set for himself eventually ground him down.
"I think that as he went on he became disenchanted with Ireland.
"He saw Ireland was never going to be at peace, he saw that people were going to keep fighting here and he was right. So he ended up spending the last ten years of his life in Italy."
The Earl Bishop may have finally given up on Ireland, but the people did not forget him.
At his ancestral home in England, where he was buried, there is a huge obelisk.
It was paid for by public subscription by Catholics, Presbyterians and Protestants of Derry.
"I don't know of any other English aristocrat or Protestant bishop who has ever had all the faiths in Ireland come together to erect a monument for him," Stephen said.
Stephen Price will present the 3D reconstructions of Hervey's works and give a talk on the Earl Bishop at the Roe Valley Arts Centre on 17 August.