evidence: Normally, it is easy to spot borders: They are marked by boundary markers, checkpoints, flags, signs and uniformed men and women. Even within the Schengen area, they are quite visible, the minimalist version being a sign telling the name of the new country. But not in Ireland, an island divided into the Republic of Ireland and Northern Ireland, the latter belonging to the United Kingdom. The inner-Irish border is a rather complicated line, based on historic county boundaries. It cuts through several villages and towns. The border stretches for 499 km (310 mi) from Carlingford Lough to Lough Foyle – more than four times the direct distance between these places. Approximately 300 roads cross it, making it maybe the world’s most permeable border. [...] That’s me arriving back in the Republic of Ireland, marked by the "Welcome to Donegal" sign, Ireland’s northernmost county. Donegal has quite a Northern Irish identity, and the island’s northernmost point is located there (and not in UK’s Northern Ireland!). [...] The border becomes obvious just on the onward journey towards Enniskillen, Fermanagh’s main town. This sign is a couple of hundred meters into Northern Ireland.