Record numbers of people from the republic visited Northern Ireland as tourists last year, up more than 50% on pre-pandemic levels.
Figures from the Central Statistics Office reveal that there were more than 800,000 such trips between January and September last year.
Hillsborough Castle in Co Down is one of the locations that has enjoyed an increase in cross-border visits.
Garrett Fitzgerald and Margaret Thatcher signed the Anglo-Irish Agreement there in 1985.
It still regularly hosts high level political encounters, with former Taoiseach Micheál Martin and former British prime minister Boris Johnson, pictured walking in its gardens while meeting there in August 2020.
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An official residence of the British monarchy, it is the only royal palace on the island of Ireland.
Its Granville rose garden is said to have been Queen Elizabeth's favourite of the many across her royal palaces and it is where her son and successor King Charles was filmed having an unfortunate accident with a leaking fountain pen during his first visit as British monarch in September.
Four years ago, the palace opened its doors and 100-acre gardens to tourists for the first time, before closing during the Covid pandemic.
Since re-opening, visits from across the border have been a strong growth area, particularly for organised coach tours.
"We find there is a real fascination in the royal family from visitors from the republic who say they love to get a glimpse behind the scenes," says Laura McCorry, Head of Hillsborough Castle.
"We get people travelling independently, but also a lot participate in organised group travel, which includes a tour of the inside of the palace. It's particularly that market that is very strong for us at the moment.
"This year already, we have got forward bookings up about 10% to 12% for visitors coming from the Republic of Ireland, so we're delighted to see that."
The Open Golf Championship in Portrush in Co Antrim in 2019 helped boost the number of visitors from the republic between January and September that year to a record figure of just over 530,000.
But that was eclipsed for the same period last year, after the lifting of restrictions, with 809,172 cross-border trips, an increase of almost 53%, according to the Central Statistics Office's Household Travel Survey.
Tourism NI believes Covid restrictions on foreign travel was a factor as it encouraged people to "staycation".
"When I look back to 2015 when we basically really started to target the Republic of Ireland market, the visitor numbers have actually trebled since that time," says Tourism NI's Chief Executive John McGrillen.
"During the first nine months of last year the visitor numbers increased by 53% on the same period in the year before the pandemic.
"I think that during the Covid period, people started to explore Northern Ireland because many of them hadn't been there before. 50% of the people who came here had come for the first time and I think what they found, they liked."
Spending by visitors from the republic also increased sharply, up more than £66 million, or almost 70%.
While city breaks to Belfast and Derry continue to be popular, one of the trends in recent years has been the number of people engaging in outdoor tourism like walking tours, hiking and glamping.
Glamping company Further Space has pods on seven sites across Northern Ireland, as well as sites at Forth Mountain in Co Wexford and Belmullet in Co Mayo.
David Maxwell, one of the co-owners, says enquiries and bookings from the Republic are increasing significantly.
"Since October last year the Republic of Ireland has represented the highest number of visitors," he explains.
"In fact, since January of this year, 60% of all of our web traffic was from the republic. If you take our social media, 65% of our social media followers are from the Republic, and 25% of that 65% is from Dublin, so we see the Republic of Ireland as a massive growth area."
