The causeway and bridge linking Leitir Móir to Garmna
The R374 connects the village of Casla (home to RTÉ Raidió na Gaeltachta) to Leitir Mealláin in County Galway. Starting from a junction with the R343 at Doire an Fhéich on the western edge of Casla, the road runs first northwestward, then turns southwest to link a number of islands by causeway and bridge, terminating at an end-on junction with local road L5324 at the post office in Leitir Mealláin.
All the communities served by the R374 lie within the County Galway Gaeltacht, and all placenames are therefore signed in Irish only. The anglicized versions of the route's end-points are "Costelloe" and "Lettermullan" (the first of these is, however, less used).