Errigal is a 751-metre mountain near Gweedore in County Donegal, Ireland. It is the tallest peak of the Derryveagh Mountains and the tallest peak in County Donegal. Errigal is also the most southern and the highest of the mountain chain called the "Seven Sisters" by locals. Wikipedia
there are some places around towns that have these kind of postal boxes built in a wall. Very convenient for the people who live around there. This one was seen in Buncrana.