To access Irish 1:50,000 maps online for free:
Go to: https://heritagedata.maps.arcgis.com/ap ... 436d8f60f8
In the top right corner click on the four boxes and change the Basemap Gallery to Discovery MapGenie (ITM)
(Also worth going to the layer List and unticking Sites and Monuments / Architectural Heritage)
If you need an exact grid ref:
In the top right of screen is a ruler - click that then 3rd box - location. This allows you to place a cursor on map with lat/long given.
Not all Irish trigs are shown on the current maps, but it can help with locations if needed. This all works well on a desktop but not great on a phone - but easy to take screenshots and download them.