Try to find the spot where the photographer was standing.
It's still standing:
Not a railway viaduct but part of the Coast Rd project
https://www.flickr.com/photos/184711311@N04 I had wrongly presumed railway!
"The Glendun Viaduct known locally as ‘The Big Bridge’ was built between 1834 and 1839 as part of the Coast Road project. It spans the river Dun in the centre of the glen and is reputed to be one of the finest structures of its kind in The British Isles. The engineer for the coast road was William Bald and his surveyor was Sir Charles Lanyon. ..."
More history - antrimhistory.net/whats-that-the-glendun-viaduct/#:~:text....
Streetview is a bit patchy and wooded around there, so here is Satellite 3D - firstname.lastname@example.org,-6.1003181,44a,35y,96.87h...
A couple of nearby Royal plates -
catalogue.nli.ie/Record/vtls000039946 (long view)
catalogue.nli.ie/Record/vtls000324594 (reverse view from on top of the bridge)
Bridges and buildings built by Irish convicts "transported" to Van Diemen's Land, by the British are still standing.
Not much dateable in nearby shots. L_ROY_02292 looks like Jaunty by the sea, so 1890s?
that's a great photo
https://www.flickr.com/photos/66151649@N02/ Yes, great shot, nobody else seems able to get one as good.
https://www.flickr.com/photos/184711311@N04 I must visit Ireland one day, scenic and so lovely.
Locals will already know all this, but I wondered why such a substantial non-railway bridge was built in the middle of nowhere over a relatively small river. Department of Sledgehammers & Nuts? No, the viaduct was part of a large project, the Antrim Coast Road -
"... a great project was conceived as a ‘grand military way’ to give better access after the 1798 rebellion. It opened up the Glens, and gave some form of unemployment relief in the days just before the 1845 potato famine. ... "
From - www.burntisland.net/bald-orr-road.pdf
More - www.causewaycoastalroute.com/antrim-coast-road
William Bald's ggg-granddaughter visits - www.bbc.com/news/uk-northern-ireland-37575993
Mr French / Lawrence seems to have visited this bridge several times ...
A couple of mistitled Cabinet photos taken on the same day (by that sharp shadow on the road, and the striped field on the left) -
Different, later date (by vegetation), with a party of tourists, NB woman in white -
catalogue.nli.ie/Record/vtls000336488 (group up on the bridge)
catalogue.nli.ie/Record/vtls000336487 (group posing on a side car)
catalogue.nli.ie/Record/vtls000336486 (more posing)
Different larger party -
And some Imperial plates (later? than today's photo) -
I think today's photo is the earliest visit on a particularly clear fine day.
ps I am not convinced that is Mr Jaunty - in my humble he is not over-dressed well-tailored and slim enough!
Great feat of engineering, whatever it took in securing the realm, and time for a photo or two? Nice to be British in 19th Century Ireland.