Fastnet Rock is off Co Cork in SW Ireland, the Republic of Ireland, that is, which is not part of the UK but a sovereign nation of its own. SW Ireland happens to be one of the most scenic parts of the world I've ever been to and I'd highly recommend a visit.

Six of the counties in the NE corner of Ireland constitute Northern Ireland, which is part of the UK. The coast of Northern Ireland is also pretty amazing.

Obviously Dermot knows all this--just info for anyone interested.