Cloghane (An Clochan in Irish), Co. Kerry, Dingle Peninsula. In 2010, I visited Chloghan as part of a 100-mile walk on the Dingle Way trail (https://www.dingleway.com/), and it instantly because my favorite small Irish town. Chloghan barely gets any tourists because it's on the north, Atlantic Ocean-facing coast of the peninsula with most visitors going to the south, Dingle Bay-facing coast where Dingle Town is located. It's coastal and sits in the shadow of Mount Brandon, the eighth-tallest mountain in Ireland. Irish speakers abound in Dingle. The town probably has 200 residents. However, if you will have access to a car, Dingle Town (population 1,500) is probably 20 minutes away. You can probably catch a bus or Uber.
Dunquin, Kerry, Dingle: This is a small town at the western edge of Dingle. A decent amount of tourists pass through because its on the western tip of the peninsula, but nothing extraordinary. It's one of two towns in my five visits to Ireland where I heard Irish spoken in everyday talk among locals.
Letterkenny, Co. Donegal: In 1997, I spent a night in Letterkenny. Virtually all of Donegal has Irish speakers. It's not on the sea, but the Atlantic is only 10 miles away. The town has a population of 20,000.
Erris, Co. Mayo: I passed through here in 1997, too. It feels very remote. Irish is spoken. It's on the sea. Few tourists visit here.