Duncannon Fort
Duncannon Fort is in the south-east corner of Ireland and is run by Wexford County Council. It has recently been released from the military and a trust set up to restore the work to its former glory. The site dates back to the 16th century but the defences and some building are as modern as WW2.
I have not seen mention of this in any guide book but it is a lovely site to visit and personal guided tours are offered.
Location: Irish NGR; S7308