The phrase "ancient mansion" is correct and usable in written English.
You can use it to describe a large, old house that has historical significance or architectural value.
Example: "The tour guide led us through the ancient mansion, sharing stories of its former inhabitants and the events that took place within its walls."
Alternatives: "historic estate" or "old manor".
Descending via stairs some 30 feet below street level, it's possible to walk along the original Roman alleyway that once separated the oldest building from its neighbor and to wander through the rooms of the ancient mansion, much as a Roman might have done two thousand years ago.
However, the occupants of this ancient mansion are no longer in control of their own destiny.
There was a great musical crash at Cambridge, which was greatly admired, but I was not there, being much better pleased with hearing my Harriote on her spinnet & organ at her ancient mansion", suggesting that he was living permanently in Market Downham, London.
The capital of ancient Portucale till the 12th century, this buzzy little university town has an exquisite medieval centre – a Unesco World Heritage Site – of ancient mansions, churches, squares and a couple of museums, all overlooked by an impressive 10th-century castle with seven castellated towers.
Toward nightfall, I noticed a billboard that advertised an ancient feudal mansion with good country food.
And as I began my hike on the narrow trail into this land of ancient rock slides, mansion-sized boulders and knife-edge drops, I began to appreciate the patience and resolve of the pioneer adventurers.
The family never went on holiday except to a holiday home at Stansgate in Essex, which was not, as newspapers often implied, an ancient castle or mansion but a prefabricated house bought by his grandfather for £600.
Some vineyards come with ancient castles or classic mansions.
Shaped like an upside-down Y, Lake Como's winding shoreline is surrounded by lush gardens, ancient villages and sprawling mansions.
Photographer Cathrine Wessel captured the country's bright neighborhoods and markets, including the Tunis medina (pictured), a magnificent jumble of ancient mosques, Ottoman-era mansions, cafés and overflowing shops.
The classical courtyard mansions and other ancient buildings are much more common in China's capital than Taiwan's capital.
