Lots of people cross the border into Northern Ireland every day. For work, for school, for holidays.
While there are some noticeable differences - speed limits change from kilometres to miles and the currency goes from sterling to euro - often it is impossible to identify the actual frontier.
It is an open border with no checkpoints and no showing of passports.
However, it was not always like that. During the Troubles, it was no easy crossing, it was a hard border.
If, as planned, the United Kingdom leaves the European Union on 31 October, the island of Ireland will have the only land border between the EU and the UK.
That border between the Republic and Northern Ireland is 499 kilometres long with around 300 crossing points.
How did the border come to be? What is its history and how might Brexit affect it? Are we looking at going back to a hard border?
news2day, RTÉ's dedicated TV news programme for children, has been finding out.
news2day is on air on RTÉ2 television at 4.20pm and is available on the RTÉ Player.