An appeal over rights-of-way at the Lissadell estate in Co Sligo is under way at the Supreme Court.
The appeal has been taken by barristers Constance Cassidy and Edward Walsh, the owners of Lissadell, against the High Court judgment of Justice Bryan McMahon, delivered in December 2010.
Judge McMahon dismissed their proceedings brought against Sligo County Council concerning the alleged existence of rights of way.
The owners are also appealing an award of costs against them of the lengthy High Court proceedings, which ran for 58 days and are estimated at around €6m.
The case was initiated after the council passed a resolution in December 2008 to amend the county development plan to include a provision for the "preservation of the public rights of way" along certain routes at Lissadell.
In their action, the couple claimed four routes through the 410-acre estate were not subject to any public rights of way but Justice McMahon disagreed.
He ruled, while the public rights of way exist, they should continue to be used only during daylight hours as had been the situation in the past.
Opening the case on behalf of the couple, Senior Counsel Brian Murray said the main thrust of their appeal was on the basis that the trial judge had erred in law in a number of respects.
They would also argue that the county council's case was "sparse and thin".
The council was effectively saying the creation of four routes in the past 150 years would have meant there was an event of immense historical interest whereby a private landowner of what was originally a 32,000 acre estate, in an act of "unprecedented munificence" ,dedicated public access to his estate, Mr Murray said.
This included a route which came right up to the door of Lissadell House despite the fact that the original house had been rebuilt and the estate reconfigured to ensure privacy for the house, he said.
The hearing is expected to last ten days before the five-judge Supreme Court.
The Lissadell estate was previously the home of the Gore Booth family for 400 years.
Constance Gore Booth, later Countess Markievicz, was Ireland's first woman Government minister, while the poet WB Yeats was a frequent visitor to Lissadell.
Ms Cassidy and Mr Walsh bought the estate in 2003 for €4m and spent €9.5m restoring it.