Here in my hometown of Aberystwyth we have a couple of "abandoned" relics from the Second World War.
Overlooking the Harbour entrance is a Pillbox/Machine gun post, presumably manned by the Home Guard.
We are also home to the National Library of Wales, which sits halfway up a hill, overlooking the town, during ww2, they built bunkers/tunnels beneath it to store their most valuable possessions, and at one point many of the UK's most valuable pieces of art, and the Crown Jewels were stored there.
We have plenty of more traditional relics of the past, such as a medieval Castle, part of Edward 1st's "Ring of Iron" around North Wales, an Iron Age Hill Fort, who's trenches in which the walls stood are still visible and so on.
We did also have an intact Tollhouse, from the days of Toll's to use the roads entering/leaving down, built in 1771, sadly, the thieving swine in Cardiff stole it, I think in the 1970's, dismantling it brick by brick and rebuilt it in the Saint Fagan's National Museum of Wales.
Tollhouse
It's very nice, I am sure that visitors to Cardiff get to see bits of Ceredigion's heritage, but it would be even nicer if the children and people of Ceredigion didn't have to travel 4 hours south to see their own heritage.
Sadly, up here its a common theme, the theft of things by Cardiff. When I was growing up we had a world famous International Film Festival, people from down South took over, and immediately moved it to Cardiff, where it seems to have vanished - a generic film festival in a City is probably not quite the same draw as one taking place in a beautiful university town/seaside resort surrounded by hills, where one can go and watch the dolphins play in between films. Another student film festival was snatched by Cardiff recently, and I doubt the Horror film festival will survive long unkidnapped.
Cardiff was even trying to grab the Celtic Challenge, a row boat race between Aberystwyth & Arklow in Ireland, despite the fact that one of the major points of the race is its 80 miles direct line between the two towns, whilst Cardiff to anwhere in Eire would be at the very least 200+ miles, and not remotely a straight line!